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

> An attacker can force a server using phpseclib to make unauthorized internal network requests during X.509 certificate validation, potentially accessing sensitive internal services.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Jun 2026
- **Updated:** 23 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-55599, GHSA-m557-wrgg-6rp4, MINI-27w4-fvmx-4237, MINI-4xrp-5fg3-x828, MINI-m36r-q9v9-2x3c, UBUNTU-CVE-2026-55599

## What is CVE-2026-55599?

CVE-2026-55599 is a medium-severity server-side request forgery vulnerability in phpseclib, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-55599?

6 open source packages ship an affected version, including phpseclib/phpseclib. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `phpseclib/phpseclib` | Packagist | From 0.1.1 | 1.0.30 |
| `phpseclib/phpseclib` | Packagist | From 0.1.1 | 1.0.30 |
| `phpseclib/phpseclib` | Packagist | From 2.0.0 | 2.0.55 |
| `phpseclib/phpseclib` | Packagist | From 2.0.0 | 2.0.55 |
| `phpseclib/phpseclib` | Packagist | From 3.0.0 | 3.0.54 |
| `phpseclib/phpseclib` | Packagist | From 3.0.0 | 3.0.54 |

Products: Phpseclib Phpseclib.

## How do I fix CVE-2026-55599?

Upgrade phpseclib/phpseclib to a fixed version for your release line: 1.0.30, 2.0.55 or 3.0.54.

## Is CVE-2026-55599 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55599 exists.

## Other vulnerabilities in phpseclib

- [CVE-2026-32935](https://insights.sbomify.com/CVE-2026-32935/): phpseclib's AES-CBC unpadding susceptible to padding oracle timing attack (high 8.2)
- [CVE-2023-52892](https://insights.sbomify.com/CVE-2023-52892/): Name confusion in x509 Subject Alternative Name fields (high 7.5)
- [CVE-2023-49316](https://insights.sbomify.com/CVE-2023-49316/): Phpseclib needs guardrails on large binaryfield integers (high 7.5)
- [CVE-2023-27560](https://insights.sbomify.com/CVE-2023-27560/): phpseclib Infinite Loop vulnerability (high 7.5)
- [CVE-2026-40194](https://insights.sbomify.com/CVE-2026-40194/): phpseclib has a variable-time HMAC comparison in SSH2::get_binary_packet() using != instead of hash_equals() (low 3.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55599 and fix it if it is affected.

What it is: CVE-2026-55599 is a medium-severity server-side request forgery vulnerability in phpseclib, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55599 exists.

Affected packages and fixed versions:
- phpseclib/phpseclib (Packagist): affected from 0.1.1; fixed in 1.0.30
- phpseclib/phpseclib (Packagist): affected from 0.1.1; fixed in 1.0.30
- phpseclib/phpseclib (Packagist): affected from 2.0.0; fixed in 2.0.55
- phpseclib/phpseclib (Packagist): affected from 2.0.0; fixed in 2.0.55
- phpseclib/phpseclib (Packagist): affected from 3.0.0; fixed in 3.0.54
- phpseclib/phpseclib (Packagist): affected from 3.0.0; fixed in 3.0.54

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-2026-55599/ (Markdown: https://insights.sbomify.com/CVE-2026-55599/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55599
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55599
- OSV: https://osv.dev/vulnerability/CVE-2026-55599

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55599/
Summaries are generated and may contain mistakes; the official description above is the record.