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
References
Configurations
No configuration.
History
18 Jul 2026, 14:17
| Type | Values Removed | Values Added |
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Information
Published : 2026-07-18 14:17
Updated : 2026-07-20 20:16
NVD link : CVE-2026-9323
Mitre link : CVE-2026-9323
CVE.ORG link : CVE-2026-9323
JSON object : View
Products Affected
No product.
CWE
CWE-338
Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)