How severe is CVE-2026-55599?

CVE-2026-55599 has a CVSS 3.x base score of 5.8, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2026-55599 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (3rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-55599?

CVE-2026-55599 affects Phpseclib. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-55599?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-55599 have an EU (EUVD) identifier?

Yes. CVE-2026-55599 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38348.

When was CVE-2026-55599 published?

CVE-2026-55599 was published on 2026-06-22 and last updated on 2026-06-26.

CVE-2026-55599

CVE-2026-55599 is a medium-severity vulnerability in Phpseclib with a CVSS 3.x base score of 5.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-918.

Key facts

Severity: Medium (CVSS 3.x base score 5.8)
EPSS exploit prediction: 0% (3rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-38348
Weakness: CWE-918
Affected product: Phpseclib
Published: 2026-06-22
Last modified: 2026-06-26

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-55599?: CVE-2026-55599 has a CVSS 3.x base score of 5.8, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2026-55599 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (3rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-55599?: CVE-2026-55599 affects Phpseclib. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-55599?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-55599 have an EU (EUVD) identifier?: Yes. CVE-2026-55599 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38348.
When was CVE-2026-55599 published?: CVE-2026-55599 was published on 2026-06-22 and last updated on 2026-06-26.

References

https://github.com/phpseclib/phpseclib/security/advisories/GHSA-m557-wrgg-6rp4

Affected products (1)

cpe:2.3:a:phpseclib:phpseclib:*:*:*:*:*:*:*:*

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