Apache::Session::Generate::ModUniqueId EUVD-2026-27823

Exploitation requires the target application to use Apache::Session::Generate::ModUniqueId (versions 1.54-1.94) for session management AND be deployed on Apache HTTP Server with mod_unique_id module enabled. The attacker must obtain at least one valid session ID through observation (network interception, browser history, application logs, or referrer leakage) to reverse-engineer the predictable components. No authentication is required-the attack is possible against any session-based functionality. Default Apache configurations do not enable mod_unique_id automatically, so exploitation is limited to environments where administrators explicitly activated this module. Applications using alternative session generators (Random, MD5, SHA256) within Apache::Session are not vulnerable. Local network positioning or man-in-the-middle capability accelerates exploitation by enabling passive session token collection, though not strictly required if tokens are observable through application features (session IDs in URLs, verbose error messages).

Real-world exploitation risk is HIGH despite absence of confirmed active exploitation. The CVSS vector AV:N/AC:L/PR:N/UI:N indicates trivial exploitation-remote attackers need no authentication, special access, or user interaction. SSVC classification confirms automatable exploitation with partial technical impact. The 9.1 CVSS score accurately reflects severity: complete confidentiality and integrity compromise (session hijacking grants full user privileges) without availability impact. While EPSS and KEV data are not provided, the automatable nature and public vulnerability details significantly increase exploitation likelihood. The attack requires only network access to observe session tokens (via cookies/URLs) and algorithmic prediction-no sophisticated exploit tooling needed. Primary risk is to web applications using affected Apache::Session versions in production with Apache httpd and mod_unique_id enabled. The deterministic nature means attackers can pre-compute valid session IDs or perform targeted hijacking by observing victim tokens and predicting nearby values. Mitigation urgency is CRITICAL for internet-facing applications handling authenticated sessions, particularly those with sensitive data or privileged operations. The vulnerability has existed since version 1.54 through 1.94, suggesting potentially widespread deployment in legacy Perl web applications.

An attacker observes a victim's session cookie (e.g., via network sniffing on shared WiFi or leaked in referrer headers). The session ID reveals server IP, approximate timestamp, and process ID through the mod_unique_id structure. The attacker writes a script to predict adjacent session IDs by incrementing the counter component and adjusting timestamps within a narrow window around the HTTP Date header value. By systematically testing predicted session tokens against the application, the attacker identifies active sessions belonging to other users and hijacks accounts with administrative privileges, accessing sensitive data or performing unauthorized transactions. Publicly available documentation of mod_unique_id's algorithm at https://httpd.apache.org/docs/current/mod/mod_unique_id.html provides the specification needed to implement prediction logic.