z-galaxy zbus_polkit up to 5.0.x Subject::new_for_owner toctou

Summaryinfo

A vulnerability categorized as very critical has been discovered in z-galaxy zbus_polkit up to 5.0.x. Affected by this vulnerability is the function Subject::new_for_owner. Executing a manipulation can lead to toctou. This vulnerability is tracked as CVE-2026-78422. The attack is restricted to local execution. No exploit exists.

Detailsinfo

A vulnerability classified as very critical was found in z-galaxy zbus_polkit up to 5.0.x. This vulnerability affects the function Subject::new_for_owner. The manipulation with an unknown input leads to a toctou vulnerability. The CWE definition for the vulnerability is CWE-367. The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability was named CVE-2026-78422 since 08/24/2026. The exploitation appears to be easy. Local access is required to approach this attack. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 08/31/2026).

Upgrading to version 5.1.0 eliminates this vulnerability.

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Productinfo

Vendor

• z-galaxy

Name

• zbus_polkit

Version

• 5.0

Website

• Product: https://github.com/z-galaxy/zbus_polkit/

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