# CVE-2026-18089: Auth bypass in Net::SAML2

> Attackers can bypass SAML authentication by embedding self-signed certificates in responses when no trust anchor is configured in the Perl library.

- **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-p5j9-p2w8-q5rw

## What is CVE-2026-18089?

CVE-2026-18089 is a high-severity authentication bypass vulnerability in TIMLEGGE Net::SAML2, published on 3 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Net::SAML2 versions before 0.86 for Perl allow SAML authentication bypass by verifying responses against the response-embedded certificate in verify_xml when no trust anchor is configured.

verify_xml in Net::SAML2::Role::VerifyXML runs "return if !$anchors && !$cacert;" as soon as the XML::Sig check succeeds, and that check uses the X.509 certificate taken from the response's own dsig:KeyInfo/dsig:X509Certificate element, so an unanchored response is checked only against the key it carries. Binding::POST declares cacert as an optional Maybe[Str] with no default, so a POST binding built without one takes that path, and _verify_encrypted_assertion returns early the same way with "return $xml unless $cacert;".

Any caller that constructs Binding::POST or calls Assertion->new_from_xml without a cacert, cert_text, or anchors argument accepts a response signed by an attacker generated key whose self-signed certificate is embedded in that response, authenticating an arbitrary assertion.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature), CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2026-18089?

It affects 1 product.


Products: Timlegge Net\.

## How do I fix CVE-2026-18089?

No fix has been published for CVE-2026-18089 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18089 being exploited?

There is no known exploitation of CVE-2026-18089 in the wild and no public exploit code.

## Other vulnerabilities in TIMLEGGE Net::SAML2

- [CVE-2026-18108](https://insights.sbomify.com/CVE-2026-18108/): Auth bypass in Net::SAML2 (critical 9.8)
- [CVE-2026-18092](https://insights.sbomify.com/CVE-2026-18092/): Auth bypass in Net::SAML2 (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18089 and fix it if it is affected.

What it is: CVE-2026-18089 is a high-severity authentication bypass vulnerability in TIMLEGGE Net::SAML2, 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-2026-18089 in the wild and no public exploit code.

Affected product: TIMLEGGE Net::SAML2. 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-2026-18089/ (Markdown: https://insights.sbomify.com/CVE-2026-18089/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18089
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18089
- OSV: https://osv.dev/vulnerability/CVE-2026-18089

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-18089/
Summaries are generated and may contain mistakes; the official description above is the record.