urwid Web Display Backend urwid/display/web.py start X-Urwid-ID random values

Summaryinfo

A vulnerability was found in urwid. It has been rated as problematic. This issue affects the function Home of the file urwid/display/web.py of the component Web Display Backend. This manipulation of the argument X-Urwid-ID causes random values. This vulnerability is registered as CVE-2026-9323. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability has been found in urwid (version unknown) and classified as problematic. Affected by this vulnerability is the function start of the file urwid/display/web.py of the component Web Display Backend. The manipulation of the argument X-Urwid-ID with an unknown input leads to a random values vulnerability. The CWE definition for the vulnerability is CWE-330. The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers. As an impact it is known to affect confidentiality. The summary by CVE is:

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

The advisory is shared at github.com. This vulnerability is known as CVE-2026-9323 since 05/22/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1600.001 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Name

• urwid

Website

• Product: https://github.com/urwid/urwid/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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