PicketLink CVE-2026-15556

The attacker must be able to submit a crafted SAML Response to the PicketLink Service Provider endpoint, which requires network access to the SP and at minimum a low-privilege position sufficient to initiate a SAML authentication flow (PR:L per CVSS vector). The SP must be using PicketLink for SAML 2.0 federation - environments not using PicketLink as their SP layer are not affected. The flaw is in SP-side assertion signature validation, so the vulnerability is present regardless of which Identity Provider is in use. Exploitation is limited by the requirement to reach the SAML ACS (Assertion Consumer Service) endpoint and inject a structurally valid but assertion-empty response; network segmentation placing the SP behind an authenticated perimeter reduces exposure. No special non-default configuration is required beyond the use of PicketLink for SAML SP processing.

The CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N) scores 8.1 and signals a high-severity, low-complexity network attack requiring only low-level privileges - consistent with a scenario where the attacker must first initiate a legitimate SAML flow (obtaining a low-privileged session) before injecting a crafted response. The high confidentiality and integrity sub-scores reflect full impersonation capability: an attacker can present forged identity and role claims, accessing any resource the SP protects. EPSS data is not present in the provided input, so exploitation probability cannot be quantified from that signal; the absence of a KEV listing means confirmed active exploitation is not established. No public POC has been identified in the provided references. Despite the absence of confirmed exploitation, the attack complexity is genuinely low - the manipulation involves structurally omitting assertion elements, a technique well understood in the SAML security research community - meaning even a mid-sized IT team should treat this as urgent given the authentication bypass potential. The DoS and JWT tags in the source data conflict with the described impact and should be treated as erroneous metadata rather than additional threat signals.

An attacker with a low-privileged account on the protected application initiates a standard SAML authentication flow, then intercepts or crafts a SAML Response containing zero assertion elements and a superficially valid signature structure. Because the PicketLink SP signature validation loop finds no assertions to check, it passes the response as valid; the attacker's forged identity and role claims - including administrative roles - are accepted, granting full access to the application.