Headline
CVE-2023-40184: Improper handling of session establishment errors allows bypassing OS-level session restrictions
xrdp is an open source remote desktop protocol (RDP) server. In versions prior to 0.9.23 improper handling of session establishment errors allows bypassing OS-level session restrictions. The auth_start_session function can return non-zero (1) value on, e.g., PAM error which may result in in session restrictions such as max concurrent sessions per user by PAM (ex ./etc/security/limits.conf) to be bypassed. Users (administrators) don’t use restrictions by PAM are not affected. This issue has been addressed in release version 0.9.23. Users are advised to upgrade. There are no known workarounds for this issue.
Affected versions
< 0.9.23
Description
Impact
Session restrictions such as max concurrent sessions per user by PAM (ex ./etc/security/limits.conf) are bypassed because of improper handling inside xrdp-sesman. Users (administrators) don’t use restrictions by PAM are not affected.
Patches
A fix has been prepared and will be released as v0.9.23.
Related news
Ubuntu Security Notice 6474-1 - It was discovered that xrdp incorrectly handled validation of client-supplied data, which could lead to out-of-bounds reads. An attacker could possibly use this issue to crash the program or extract sensitive information. It was discovered that xrdp improperly handled session establishment errors. An attacker could potentially use this issue to bypass the OS-level session restrictions by PAM.