Vulnerability-Lookup

GHSA-CG68-CM33-8VQV

Vulnerability from github – Published: 2026-08-13 18:31 – Updated: 2026-08-13 21:36

Details

Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass.

The prescan walks the subject for positions where the full pattern could match, and the engine tries it from the leftmost one recorded. A failing transition sets the failed flag, and a later successful transition does not clear it, so the prescan reads the stale flag as a failure and stops before it can record a candidate that starts earlier. It takes a subject where one candidate is recorded and a later character then forces a fallback through a fail link that succeeds.

Example:

"ABCDE" =~ m/ABCF|BCDE|C/; # matches C at offset 2, not BCDE "ABCDE" =~ m/ABCF|BCDE|C(G)/; # no match, BCDE missed

An alternation like this can miss input it should match, or match it on the wrong branch, so an access or filtering decision made from the result can be wrong.

Severity

5.3 (Medium)


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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-19487"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-670"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-13T16:17:59Z",
    "severity": "MODERATE"
  },
  "details": "Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass.\n\nThe prescan walks the subject for positions where the full pattern could match, and the engine tries it from the leftmost one recorded. A failing transition sets the failed flag, and a later successful transition does not clear it, so the prescan reads the stale flag as a failure and stops before it can record a candidate that starts earlier. It takes a subject where one candidate is recorded and a later character then forces a fallback through a fail link that succeeds.\n\nExample:\n\n  \"ABCDE\" =~ m/ABCF|BCDE|C/;    # matches C at offset 2, not BCDE\n  \"ABCDE\" =~ m/ABCF|BCDE|C(G)/; # no match, BCDE missed\n\nAn alternation like this can miss input it should match, or match it on the wrong branch, so an access or filtering decision made from the result can be wrong.",
  "id": "GHSA-cg68-cm33-8vqv",
  "modified": "2026-08-13T21:36:04Z",
  "published": "2026-08-13T18:31:37Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-19487"
    },
    {
      "type": "WEB",
      "url": "https://github.com/Perl/perl5/issues/22892"
    },
    {
      "type": "WEB",
      "url": "https://github.com/Perl/perl5/commit/1a21abacaf6f684928bae8baaa153733c8c238eb.patch"
    },
    {
      "type": "WEB",
      "url": "http://www.openwall.com/lists/oss-security/2026/08/13/8"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-19487 (GCVE-0-2026-19487)

Vulnerability from cvelistv5 – Published: 2026-08-13 15:51 – Updated: 2026-08-13 20:12

Title

Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass

Summary

Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass. The prescan walks the subject for positions where the full pattern could match, and the engine tries it from the leftmost one recorded. A failing transition sets the failed flag, and a later successful transition does not clear it, so the prescan reads the stale flag as a failure and stops before it can record a candidate that starts earlier. It takes a subject where one candidate is recorded and a later character then forces a fallback through a fail link that succeeds. Example: "ABCDE" =~ m/ABCF|BCDE|C/; # matches C at offset 2, not BCDE "ABCDE" =~ m/ABCF|BCDE|C(G)/; # no match, BCDE missed An alternation like this can miss input it should match, or match it on the wrong branch, so an access or filtering decision made from the result can be wrong.

Severity

5.3 (Medium)


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

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-13 17:47 UTC

CWE

CWE-670 - Always-Incorrect Control Flow Implementation

Assigner

CPANSec

References

3 references

URL	Tags
https://github.com/Perl/perl5/commit/1a21abacaf6f…	patch
https://github.com/Perl/perl5/issues/22892	issue-tracking
http://www.openwall.com/lists/oss-security/2026/08/13/8

Impacted products

1 product

Vendor	Product	Version
		Affected: 5.9.4 , < 5.41.9 (custom)

Show details on NVD website

JSON

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{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "cvssV3_1": {
              "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"
            }
          },
          {
            "other": {
              "content": {
                "id": "CVE-2026-19487",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-13T17:47:48.584748Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-08-13T17:48:30.123Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/Perl/perl5/issues/22892"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      },
      {
        "providerMetadata": {
          "dateUpdated": "2026-08-13T20:12:11.045Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
        },
        "references": [
          {
            "url": "http://www.openwall.com/lists/oss-security/2026/08/13/8"
          }
        ],
        "title": "CVE Program Container"
      }
    ],
    "cna": {
      "affected": [
        {
          "collectionURL": "https://cpan.org/modules",
          "defaultStatus": "unaffected",
          "modules": [
            "perl"
          ],
          "packageName": "perl",
          "packageURL": "pkg:cpan/perl",
          "programFiles": [
            "regexec.c"
          ],
          "programRoutines": [
            {
              "name": "S_find_byclass"
            }
          ],
          "repo": "https://github.com/Perl/perl5",
          "versions": [
            {
              "lessThan": "5.41.9",
              "status": "affected",
              "version": "5.9.4",
              "versionType": "custom"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass.\n\nThe prescan walks the subject for positions where the full pattern could match, and the engine tries it from the leftmost one recorded. A failing transition sets the failed flag, and a later successful transition does not clear it, so the prescan reads the stale flag as a failure and stops before it can record a candidate that starts earlier. It takes a subject where one candidate is recorded and a later character then forces a fallback through a fail link that succeeds.\n\nExample:\n\n  \"ABCDE\" =~ m/ABCF|BCDE|C/;    # matches C at offset 2, not BCDE\n  \"ABCDE\" =~ m/ABCF|BCDE|C(G)/; # no match, BCDE missed\n\nAn alternation like this can miss input it should match, or match it on the wrong branch, so an access or filtering decision made from the result can be wrong."
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-670",
              "description": "CWE-670 Always-Incorrect Control Flow Implementation",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-13T15:51:04.090Z",
        "orgId": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
        "shortName": "CPANSec"
      },
      "references": [
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/Perl/perl5/commit/1a21abacaf6f684928bae8baaa153733c8c238eb.patch"
        },
        {
          "tags": [
            "issue-tracking"
          ],
          "url": "https://github.com/Perl/perl5/issues/22892"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "Upgrade to Perl 5.42.0 or later, or apply the upstream patch."
        }
      ],
      "source": {
        "discovery": "UNKNOWN"
      },
      "title": "Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass",
      "x_generator": {
        "engine": "cpansec-cna-tool 0.1"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
    "assignerShortName": "CPANSec",
    "cveId": "CVE-2026-19487",
    "datePublished": "2026-08-13T15:51:04.090Z",
    "dateReserved": "2026-08-10T16:35:50.763Z",
    "dateUpdated": "2026-08-13T20:12:11.045Z",
    "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.

Action not permitted

GHSA-CG68-CM33-8VQV

CVE-2026-19487 (GCVE-0-2026-19487)

Tags

Sightings

Nomenclature