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CVE-2026-55599

5.8 · MEDIUM

phpseclib is a PHP secure communications library.

Published Jun 22, 2026CWE-918EPSS 0.21%

Overview

CVE-2026-55599 is a medium-severity vulnerability. It was published on June 22, 2026 and has a CVSS 3.1 base score of 5.8 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.8, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/phpseclib/phpseclib/security/advisories/GHSA-m557-wrgg-6rp4GitHubgithub.com/phpseclib/phpseclib/security/advisories/GHSA-m557-wrgg-6rp4

How CyberStrike helps

Frequently asked questions

What is CVE-2026-55599?

CVE-2026-55599 is a medium-severity vulnerability. It was published on June 22, 2026 and has a CVSS 3.1 base score of 5.8 (MEDIUM).

How severe is CVE-2026-55599?

This vulnerability has a CVSS 3.1 base score of 5.8, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-55599?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-55599?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-55599 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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