# CVE-2026-68278: drm/dp/mst: fix buffer overflows in sideband chunk accumulation

> A malicious DP MST device can trigger buffer overflows in the Linux kernel sideband handler, potentially leading to code execution or system crash.

- **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:** 10 Aug 2026
- **Updated:** 23 Aug 2026
- **Also known as:** BELL-CVE-2026-68278, DEBIAN-CVE-2026-68278, GHSA-4w62-3fjj-vmpc, UBUNTU-CVE-2026-68278

## What is CVE-2026-68278?

CVE-2026-68278 is a memory corruption vulnerability in Linux, published on 10 Aug 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:

drm/dp/mst: fix buffer overflows in sideband chunk accumulation

drm_dp_sideband_append_payload() has three related bugs when processing
device-provided sideband reply data:

1. Zero-length curchunk_len underflow: msg_len is a 6-bit field taken
   directly from the DP sideband header. If a device sends msg_len=0,
   curchunk_len is set to zero. The condition (curchunk_idx >= curchunk_len)
   is immediately true, and curchunk_len-1 wraps to 255 (u8 underflow).
   drm_dp_msg_data_crc4() reads 255 bytes from chunk[48], then memcpy()
   writes 255 bytes into msg[], both far out of bounds.

2. chunk[48] overflow: curchunk_len can reach 63 (6-bit field). chunk[] is
   only 48 bytes. Multi-iteration payload assembly appends 16-byte blocks
   until curchunk_idx reaches curchunk_len, writing up to 15 bytes past
   the end of chunk[] into msg[].

3. msg[256] overflow: each chunk contributes (curchunk_len-1) bytes to
   msg[]. No check ensures curlen + (curchunk_len-1) stays within msg[256],
   so the memcpy can spill into adjacent struct fields.

All three are reachable from any DP MST device that can forge sideband
reply messages on a physical connection.

## Which versions are affected by CVE-2026-68278?


## How do I fix CVE-2026-68278?

Apply the vendor's patch.

## Is CVE-2026-68278 being exploited?

There is no known exploitation of CVE-2026-68278 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68278 and fix it if it is affected.

What it is: CVE-2026-68278 is a memory corruption vulnerability in Linux, published on 10 Aug 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-2026-68278 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-2026-68278/ (Markdown: https://insights.sbomify.com/CVE-2026-68278/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68278
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68278
- OSV: https://osv.dev/vulnerability/CVE-2026-68278

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68278/
Summaries are generated and may contain mistakes; the official description above is the record.