CVE-2025-34090

A security bypass vulnerability exists in Google Chrome AppBound cookie encryption mechanism due to insufficient validation of COM server paths during inter-process communication. A local low-privileged attacker can hijack the COM class identifier (CLSID) registration used by Chromes elevation service and point it to a non-existent or malicious binary. When this hijack occurs, Chrome silently falls back to the legacy cookie encryption mechanism (protected only by user-DPAPI), thereby enabling cookie decryption by any user-context malware without SYSTEM-level access. This flaw bypasses the protections intended by the AppBound encryption design and allows cookie theft from Chromium-based browsers.

Confirmed in Google Chrome with AppBound Encryption enabled. Other Chromium-based browsers may be affected if they implement similar COM-based encryption mechanisms.

Weakness

During installation, installed file permissions are set to allow anyone to modify those files.

Potential Mitigations

• Compartmentalize the system to have “safe” areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
• Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/1.html
• https://cwe.mitre.org/data/definitions/127.html
• https://cwe.mitre.org/data/definitions/81.html

References

• https://vulncheck.com/advisories/google-chrome-appbound-cookie-encryption
• https://www.cyberark.com/resources/threat-research-blog/c4-bomb-blowing-up-chromes-appbound-cookie-encryption