Bug 2526327 (CVE-2026-78422)

Summary: CVE-2026-78422 zbus_polkit: zbus_polkit: Privilege escalation via PID reuse due to incorrect D-Bus type handling
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in zbus_polkit. The `Subject::new_for_owner()` function incorrectly encodes the user ID (UID) as an unsigned 32-bit integer instead of a signed 32-bit integer when communicating with the PolicyKit (polkit) authorization framework. This type mismatch causes polkit to disregard the provided UID and instead determine the subject's owner by looking up the process ID (PID) in `/proc`. A local unprivileged attacker can exploit a time-of-check/time-of-use (TOCTOU) race condition by terminating an authorized process and then reusing its PID, thereby bypassing polkit authorization and gaining unauthorized privileges.
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Bug Depends On: 2526475, 2526476, 2526477, 2526479    
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Description OSIDB Bzimport 2026-08-31 14:32:01 UTC 
Subject::new_for_owner() in the zbus_polkit crate encodes the uid entry of a unix-process polkit subject as an unsigned 32-bit integer (D-Bus type u), whereas the org.freedesktop.PolicyKit1.Authority interface specifies a signed 32-bit integer (D-Bus type i). Because of this type mismatch, polkit silently discards the caller-supplied UID and instead determines the subject's owner itself by looking up the PID in /proc, a lookup that is inherently subject to a time-of-check/time-of-use race.

Consequently, an application that passes a UID obtained from a trustworthy source — for example SO_PEERCRED Unix socket peer credentials — in order to defend against PID reuse receives no protection, and the supplied UID has no effect on the authorization decision. A local unprivileged attacker who can cause an authorized process to terminate and then win the race to have their own process assigned the same PID can be authorized under the identity of the terminated process, bypassing the polkit authorization check and performing actions the attacker is not entitled to.

This issue affects zbus_polkit before 5.1.0.