CVE-2026-9323 Insecure PRNG and Information Exposure in urwid Web Display Backend

What is CVE-2026-9323?

CVE-2026-9323 is a critical vulnerability in urwid, published on 18 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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

Weakness: CWE-338

Which versions are affected by CVE-2026-9323?

How do I fix CVE-2026-9323?

Apply the vendor's patch.

Is CVE-2026-9323 being exploited?

There is no known exploitation of CVE-2026-9323 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• GitHub advisory
• How this page is made

Also known as ALSA-2026:58561, ALSA-2026:58562, ALSA-2026:58952, AZL-92916, BELL-CVE-2026-9323, DEBIAN-CVE-2026-9323 and 22 more.