XML::Sig versions from 0.29 before 0.72 for Perl allow signature verification bypass because verify returns true when every signature was skipped before any cryptographic check

{
  "id": "c47b77fca8934468f0490f945c03b8462b1c439ce77fceb43eed1b4ec640130e",
  "url": "https://osv.dev/vulnerability/CVE-2026-18568",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "XML::Sig versions from 0.29 before 0.72 for Perl allow signature verification bypass because verify returns true when every signature was skipped before any cryptographic check",
    "summary": "XML::Sig versions from 0.29 before 0.72 for Perl allow signature verification bypass because verify returns true when every signature was skipped before any cryptographic check. verify in lib/XML/Sig.pm counts the `//dsig:Signature` elements into `$numsigs` and iterates over them, but two paths reach `next` before any digest or key check runs: a `SignedInfo/Reference/@URI` that resolves to no element while `$numsigs` is greater than 1, and, when `id_attr` is set, a reference that does not match the requested ID. The loop records nothing about what it checked, so when every signature takes one of those paths control reaches the unconditional `return 1` that ends verify. Two `Signature` elements whose Reference URI names an ID that no element carries is enough, as is one such element combined with `id_attr`. Any caller that passes untrusted XML to verify can receive a true return for a document in which no digest and no signature value was checked; a `cert` or `cert_text` trust anchor does not change this, because no key check runs. Versions up to 0.28 use an XML::XPath based verify that has no such skip and are not affected.",
    "evidence": "osv:CVE-2026-18568",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-18568",
      "aliases": [
        "CVE-2026-18568"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/perl-net-saml2/perl-xml-sig",
              "type": "GIT",
              "events": [
                {
                  "introduced": "1b1e2fc5257d518c95b77c996a9b45a80f578766"
                },
                {
                  "fixed": "fed89d10445c64ad054d9b1820bf3e21d56ddf69"
                },
                {
                  "fixed": "ef22cfed1ac0f29b316d17eb79cf6480e03ae16a"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:xml\\:\\:sig_project:xml\\:\\:sig:*:*:*:*:*:perl:*:*",
                    "range": [
                      {
                        "introduced": "0.29"
                      },
                      {
                        "fixed": "0.72"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "ef22cfed1ac0f29b316d17eb79cf6480e03ae16a"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-18568.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:31.937136444Z",
      "provider": "osv",
      "references": [
        "https://cpan.org/modules",
        "https://www.cve.org/CVERecord?id=CVE-2025-40934",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18568.json",
        "https://metacpan.org/release/TIMLEGGE/XML-Sig-0.72/changes",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-18568",
        "https://github.com/perl-net-saml2/perl-XML-Sig/commit/ef22cfed1ac0f29b316d17eb79cf6480e03ae16a.patch",
        "https://github.com/perl-net-saml2/perl-XML-Sig"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-347"
        ],
        "cna_assigner": "CPANSec",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18568.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-18568",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 499161,
  "published_at": "2026-08-03T14:38:52.54+00:00"
}