FKIE_CVE-2026-18568
Vulnerability from fkie_nvd - Published: 2026-08-03 16:16 - Updated: 2026-08-03 20:17
Severity
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.
References
Impacted products
| Vendor | Product | Version |
|---|
{
"affected": [
{
"affectedData": [
{
"collectionURL": "https://cpan.org/modules",
"defaultStatus": "unaffected",
"packageName": "XML-Sig",
"product": "XML::Sig",
"programFiles": [
"lib/XML/Sig.pm"
],
"programRoutines": [
{
"name": "XML::Sig::verify"
}
],
"repo": "https://github.com/perl-net-saml2/perl-XML-Sig",
"vendor": "TIMLEGGE",
"versions": [
{
"lessThan": "0.72",
"status": "affected",
"version": "0.29",
"versionType": "custom"
}
]
}
],
"source": "9b29abf9-4ab0-4765-b253-1875cd9b441e"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "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.\n\nverify 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`.\n\nAny 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."
}
],
"id": "CVE-2026-18568",
"lastModified": "2026-08-03T20:17:15.077",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "NONE",
"baseScore": 7.5,
"baseSeverity": "HIGH",
"confidentialityImpact": "NONE",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
"version": "3.1"
},
"exploitabilityScore": 3.9,
"impactScore": 3.6,
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2026-18568",
"options": [
{
"exploitation": "none"
},
{
"automatable": "yes"
},
{
"technicalImpact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-08-03T20:05:13.814301Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-08-03T16:16:28.560",
"references": [
{
"source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
"url": "https://github.com/perl-net-saml2/perl-XML-Sig/commit/ef22cfed1ac0f29b316d17eb79cf6480e03ae16a.patch"
},
{
"source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
"url": "https://metacpan.org/release/TIMLEGGE/XML-Sig-0.72/changes"
},
{
"source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
"url": "https://www.cve.org/CVERecord?id=CVE-2025-40934"
}
],
"sourceIdentifier": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
"vulnStatus": "Undergoing Analysis",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-347"
}
],
"source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
"type": "Secondary"
}
]
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
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.
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