CVE-2026-63962 usb: typec: tcpm: bound altmode_desc[] per iteration in svdm_consume_modes()
A malicious USB Type-C partner can trigger a buffer overflow in the Linux kernel TCPM driver, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63962?
CVE-2026-63962 is a memory corruption vulnerability in Linux, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
usb: typec: tcpm: bound altmode_desc[] per iteration in svdm_consume_modes()
svdm_consume_modes() checks pmdata->altmodes against the array size once before the loop over the count, but forgot to check the bound at every point in the loop.
In the well-behaved SVDM discovery flow this is harmless because each of at most SVID_DISCOVERY_MAX SVIDs contributes at most MODE_DISCOVERY_MAX modes, exactly filling altmode_desc[ALTMODE_DISCOVERY_MAX]. But the CMDT_RSP_ACK handler in tcpm_pd_svdm() does not correlate an incoming ACK with any request the port actually sent. Once port->partner is set, an unsolicited Discover Modes ACK is consumed unconditionally. A broken or malicious port partner can therefore drive altmodes to ALTMODE_DISCOVERY_MAX - 1 via the normal flow, and then send one extra Discover Modes ACK with seven VDOs. Because the pre-loop check passes, the loop could then writes up to five entries past altmode_desc[]. For mode_data_prime the next field in struct tcpm_port is the partner_altmode[] pointer array, which then receives partner-chosen SVID/VDO bytes.
Move the bound check inside the loop so the array can never be indexed past ALTMODE_DISCOVERY_MAX regardless of how many VDOs the partner supplies or how the function was reached.
Which versions are affected by CVE-2026-63962?
How do I fix CVE-2026-63962?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-63962 being exploited?
There is no known exploitation of CVE-2026-63962 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-63962, DEBIAN-CVE-2026-63962, GHSA-2qj8-cjv3-rxv7, ROOT-OS-DEBIAN-11-CVE-2026-63962, ROOT-OS-DEBIAN-12-CVE-2026-63962, ROOT-OS-UBUNTU-2204-CVE-2026-63962 and 1 more.