CVE-2026-55599
phpseclib: X.509 certificate validation sends attacker-controlled outbound requests (server-side request forgery) via Authority Information Access
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.
How to fix CVE-2026-55599
To remediate CVE-2026-55599, upgrade the affected package to a fixed version below.
- —upgrade to 1.0.30 or later
Is CVE-2026-55599 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- >= 0.1.1, < 1.0.30
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM5.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N |