Vulnerability-Lookup

RHSA-2026:54481

Vulnerability from csaf_redhat - Published: 2026-08-13 07:52 - Updated: 2026-08-25 09:43

Summary

Red Hat Security Advisory: python-idna security update

Severity

Moderate

Notes

Topic: An update for python-idna is now available for Red Hat Enterprise Linux 10. Red Hat Product Security has rated this update as having a security impact of Moderate. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

Details: Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems. Security Fix(es): * python-idna: idna: Denial of Service via specially crafted long inputs (CVE-2026-45409) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Terms of Use: This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original.

CVE-2026-45409

A flaw was found in the idna library, which handles Internationalized Domain Names in Python applications. A remote attacker could exploit this vulnerability by sending specially crafted, excessively long inputs to the library's encoding function. This could cause the system to consume significant resources, leading to a Denial of Service (DoS), where the affected application becomes unavailable to legitimate users. This issue stems from an incomplete fix for a previously identified vulnerability.

5.3 (Medium)


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

CWE-770 - Allocation of Resources Without Limits or Throttling

Affected products

Fixed 2 products

Product	Identifier	Version	Remediation
Unresolved product id: BaseOS-10.2.Z:python-idna-0:3.7-6.el10_2.src		—	Vendor Fix fix Workaround
Unresolved product id: BaseOS-10.2.Z:python3-idna-0:3.7-6.el10_2.noarch		—	Vendor Fix fix Workaround

Threats

Impact Moderate

References

9 references

URL	Category
https://access.redhat.com/errata/RHSA-2026:54481	self
https://access.redhat.com/security/updates/classi…	external
https://bugzilla.redhat.com/show_bug.cgi?id=2485616	external
https://security.access.redhat.com/data/csaf/v2/a…	self
https://access.redhat.com/security/cve/CVE-2026-45409	self
https://bugzilla.redhat.com/show_bug.cgi?id=2485616	external
https://www.cve.org/CVERecord?id=CVE-2026-45409	external
https://nvd.nist.gov/vuln/detail/CVE-2026-45409	external
https://github.com/kjd/idna/security/advisories/G…	external

JSON

To clipboard

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        "name": "Allocation of Resources Without Limits or Throttling"
      },
      "discovery_date": "2026-06-05T23:01:44.292958+00:00",
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          "category": "description",
          "text": "A flaw was found in the idna library, which handles Internationalized Domain Names in Python applications. A remote attacker could exploit this vulnerability by sending specially crafted, excessively long inputs to the library\u0027s encoding function. This could cause the system to consume significant resources, leading to a Denial of Service (DoS), where the affected application becomes unavailable to legitimate users. This issue stems from an incomplete fix for a previously identified vulnerability.",
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          "text": "A flaw was found in the python-idna library. This is an incomplete fix for CVE-2024-3651. The idna.encode() function performs contextual validation checks (valid_contexto) before rejecting oversized inputs, allowing specially crafted long payloads to cause excessive CPU consumption and lead to a denial of service. The fix in version 3.14 rejects long inputs early before further processing, and version 3.15 extends this approach to alternate per-label conversion and codec functions.",
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        {
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      "remediations": [
        {
          "category": "vendor_fix",
          "date": "2026-08-13T07:52:40+00:00",
          "details": "For details on how to apply this update, which includes the changes described in this advisory, refer to:\n\nhttps://access.redhat.com/articles/11258",
          "product_ids": [
            "BaseOS-10.2.Z:python-idna-0:3.7-6.el10_2.src",
            "BaseOS-10.2.Z:python3-idna-0:3.7-6.el10_2.noarch"
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        },
        {
          "category": "workaround",
          "details": "To mitigate this denial-of-service vulnerability, applications utilizing the `idna` Python library should implement input validation to ensure that domain names do not exceed the standard 253-character length limit before being passed to the `idna.encode()` function. This operational control prevents the processing of excessively long inputs that could lead to resource exhaustion and service unavailability.\n\nApplications that pass user-controlled data directly to `idna.encode()` without validation checks (e.g.: DNS length \u003c 254 chars) are affected.",
          "product_ids": [
            "BaseOS-10.2.Z:python-idna-0:3.7-6.el10_2.src",
            "BaseOS-10.2.Z:python3-idna-0:3.7-6.el10_2.noarch"
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        }
      ],
      "scores": [
        {
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            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "LOW",
            "baseScore": 5.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
            "version": "3.1"
          },
          "products": [
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          ]
        }
      ],
      "threats": [
        {
          "category": "impact",
          "details": "Moderate"
        }
      ],
      "title": "python-idna: idna: Denial of Service via specially crafted long inputs"
    }
  ]
}

CVE-2026-45409 (GCVE-0-2026-45409)

Vulnerability from cvelistv5 – Published: 2026-06-05 22:06 – Updated: 2026-06-08 16:34

Title

Internationalized Domain Names in Applications (IDNA): Specially crafted inputs to idna.encode() can bypass CVE-2024-3651 fix

Summary

Internationalized Domain Names in Applications (IDNA) for Python provides support for Internationalized Domain Names in Applications (IDNA) and Unicode IDNA Compatibility Processing. In versions prior to 3.15, payloads such as `"\u0660" * N` or `"\u30fb" * N + "\u6f22"` utilize the `valid_contexto` function prior to length rejection, and for high values of `N` will take a long time to process. This is the same issue as CVE-2024-3651, however the original remediation in 2024 was not a complete fix. A specially crafted argument to the `idna.encode()` function could consume significant resources. This may lead to a denial-of-service. Starting in version 3.14, the function rejects long inputs as soon as practicable prior to any further processing to minimize resource consumption. In version 3.15, this approach was extended to lesser used alternate functions (i.e. per-label conversions and codec support). A workaround is available. Domain names cannot exceed 253 characters in length. If this length limit is enforced prior to passing the domain to the `idna.encode()` function, it should no longer consume significant resources. This is triggered by arbitrarily large inputs that would not occur in normal usage, but may be passed to the library assuming there is no preliminary input validation by the higher-level application.

Severity

6.9 (Medium)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-06-08 14:30 UTC

CWE

CWE-1333 - Inefficient Regular Expression Complexity

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/kjd/idna/security/advisories/G…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
kjd	idna	Affected: < 3.15

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-45409",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-08T14:30:54.406761Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
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          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "idna",
          "vendor": "kjd",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 3.15"
            }
          ]
        }
      ],
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        {
          "lang": "en",
          "value": "Internationalized Domain Names in Applications (IDNA) for Python provides support for Internationalized Domain Names in Applications (IDNA) and Unicode IDNA Compatibility Processing. In versions prior to 3.15, payloads such as `\"\\u0660\" * N` or `\"\\u30fb\" * N + \"\\u6f22\"` utilize the `valid_contexto` function prior to length rejection, and for high values of `N` will take a long time to process. This is the same issue as CVE-2024-3651, however the original remediation in 2024 was not a complete fix. A specially crafted argument to the `idna.encode()` function could consume significant resources. This may lead to a denial-of-service. Starting in version 3.14, the function rejects long inputs as soon as practicable prior to any further processing to minimize resource consumption. In version 3.15, this approach was extended to lesser used alternate functions (i.e. per-label conversions and codec support). A workaround is available. Domain names cannot exceed 253 characters in length. If this length limit is enforced prior to passing the domain to the `idna.encode()` function, it should no longer consume significant resources. This is triggered by arbitrarily large inputs that would not occur in normal usage, but may be passed to the library assuming there is no preliminary input validation by the higher-level application."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 6.9,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "LOW",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-1333",
              "description": "CWE-1333: Inefficient Regular Expression Complexity",
              "lang": "en",
              "type": "CWE"
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          ]
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      "providerMetadata": {
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      },
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          "url": "https://github.com/kjd/idna/security/advisories/GHSA-65pc-fj4g-8rjx"
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      "source": {
        "advisory": "GHSA-65pc-fj4g-8rjx",
        "discovery": "UNKNOWN"
      },
      "title": "Internationalized Domain Names in Applications (IDNA): Specially crafted inputs to idna.encode() can bypass CVE-2024-3651 fix"
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  "cveMetadata": {
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    "state": "PUBLISHED"
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  "dataType": "CVE_RECORD",
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}

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.

Action not permitted

RHSA-2026:54481

CVE-2026-45409 (GCVE-0-2026-45409)

Tags

Sightings

Nomenclature