Is CVE-2026-55599 actively exploited?

No active exploitation of CVE-2026-55599 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-55599 be exploited remotely?

Yes. CVE-2026-55599 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-55599?

CVE-2026-55599 has a CVSS score of 5.8 (MEDIUM).

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MEDIUM

CVE-2026-55599

CWE-918Published: June 22, 2026· Updated: Jun 26, 2026

5.8

CVSS v3.1

EPSS:0.13%probability of exploitation in 30 daysPercentile:2.8th

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.

NVD Source

Technical Analysis

CVE-2026-55599 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.