# CVE-2026-18568: Security feature bypass in XML::Sig

> Attackers can bypass XML signature verification in Perl XML::Sig by crafting documents that cause all signatures to be skipped, leading to acceptance of unsigned data.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 3 Aug 2026
- **Updated:** 3 Aug 2026
- **Also known as:** GHSA-r3hj-rg3j-262c

## What is CVE-2026-18568?

CVE-2026-18568 is a high-severity vulnerability in TIMLEGGE XML::Sig, published on 3 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-18568?

It affects 1 product.


Products: Xml\ \.

## How do I fix CVE-2026-18568?

No fix has been published for CVE-2026-18568 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18568 being exploited?

There is no known exploitation of CVE-2026-18568 in the wild and no public exploit code.

## Other vulnerabilities in TIMLEGGE XML::Sig

- [CVE-2025-40934](https://insights.sbomify.com/CVE-2025-40934/): XML-Sig prior to 0.68 for Perl improperly validates XML without signatures (critical 9.3)
- [CVE-2026-9390](https://insights.sbomify.com/CVE-2026-9390/): XML::Sig versions before 0.71 for Perl allow XPath injection in ID lookup (critical 9.1)
- [CVE-2026-9487](https://insights.sbomify.com/CVE-2026-9487/): XML::Sig versions before 0.71 for Perl allow signature wrapping via duplicate ID (critical 9.1)
- [CVE-2012-1102](https://insights.sbomify.com/CVE-2012-1102/): XML external entity in perl-xml-atom (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18568 and fix it if it is affected.

What it is: CVE-2026-18568 is a high-severity vulnerability in TIMLEGGE XML::Sig, published on 3 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-18568 in the wild and no public exploit code.

Affected product: TIMLEGGE XML::Sig. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-18568/ (Markdown: https://insights.sbomify.com/CVE-2026-18568/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18568
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18568
- OSV: https://osv.dev/vulnerability/CVE-2026-18568

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18568/
Summaries are generated and may contain mistakes; the official description above is the record.