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CVE-2026-18568

CVE-2026-18568 is a CWE-347 vulnerability. O3 Security confirms whether CVE-2026-18568 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

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…

Published
Aug 3, 2026
Updated
Aug 3, 2026
Affected
0 pkgs
Patched
None yet
Exploits
None indexed

Description

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.

Detection & mitigation playbook

Vulnerability

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for the affected component. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. Remediation status

    No patched version of the affected component has shipped for CVE-2026-18568 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.

  3. Mitigate without a patch

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether CVE-2026-18568 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-18568. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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
O3 Security · Impact-Aware SCA

Is CVE-2026-18568 in your dependencies?

O3 detects CVE-2026-18568 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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