CVE Catalog

CVE-2026-9323

HighCVSS 8.1
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.42%

34th percentile - higher than 34% of all known CVEs

Summary

Vulnerability in urwid web backend (urwid/display/web.py) generating session IDs using cryptographically insecure Mersenne Twister PRNG. Attacker can reconstruct PRNG state after observing ~334 IDs and predict all sessions. Also, session ID is used as FIFO filename in /tmp, allowing local users to enumerate active sessions.

Risk Assessment

Attacker can read victim's terminal screen, inject keystrokes (leading to OS-level code execution), or terminate sessions, posing serious risk to confidentiality and integrity.

Recommendation

Update urwid library to a version using a cryptographically secure random generator and avoid storing session IDs in /tmp.

Related vulnerabilities

Original NVD description (English source)

The urwid web display backend (urwid/display/web.py) generates web session identifiers (urwid_id) in Screen.start() by concatenating two random.randrange(10**9) calls that use Python's Mersenne Twister PRNG, which is not cryptographically secure. Each call consumes approximately 30 bits of PRNG state, and the Mersenne Twister internal state is approximately 19,937 bits, so an attacker who observes approximately 334 session IDs (for example via the X-Urwid-ID HTTP response header) can fully reconstruct the internal state and predict all past and future session IDs (Path B). The same identifier is also used as the filename of a FIFO created in the world-listable /tmp directory (for example /tmp/urwid375487765176907690.in), so any local user on the host can list /tmp to enumerate active session tokens directly (Path A). With a valid session ID, an attacker can read the victim's terminal screen via the polling endpoint, inject keystrokes into the victim's session (yielding OS-level code execution with the session owner's privileges if the session runs a shell), and inject exit sequences or flood the FIFO to terminate or crash the session. A prior Bandit S311 warning on this usage was suppressed with # noqa: S311 rather than fixed

Vulnerability data from NVD (NIST) · CISA KEV · EPSS