SSRF in Phpseclib

CVE-2026-55599

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.

Vulnerability class: SSRF (Server-Side Request Forgery)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.8 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.002 (10.4th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 10th percentile — 10.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-55599: held from 0.002 to 0.002.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000

Affected products

  • Phpseclib — versions >= 0.1.1, < 1.0.30, >= 2.0.0, < 2.0.55, >= 3.0.0, < 3.0.54

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-55599?
CVE-2026-55599 is a medium-severity vulnerability in Phpseclib, classified under Server-Side Request Forgery (SSRF). CVSS score: 5.8/10. Published 2026-06-22.
How severe is CVE-2026-55599?
Medium severity. CVSS v3 base score is 5.8 out of 10.