# 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.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 21 Oct 2026
- **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, UBUNTU-CVE-2026-63962

## 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.

## Is CVE-2026-63962 being exploited?

There is no known exploitation of CVE-2026-63962 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63962 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-63962 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-63962/ (Markdown: https://insights.sbomify.com/CVE-2026-63962/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63962
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63962
- OSV: https://osv.dev/vulnerability/CVE-2026-63962

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63962/
Summaries are generated and may contain mistakes; the official description above is the record.