# CVE-2026-80603: netfilter: nf_conntrack_irc: fix parse_dcc() off-by-one OOB read

> An off-by-one error in the Linux kernel's IRC conntrack module allows reading one byte of uninitialized memory, potentially leaking stale data.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-80603, DEBIAN-CVE-2026-80603, GHSA-66q8-v4rr-393c, UBUNTU-CVE-2026-80603

## What is CVE-2026-80603?

CVE-2026-80603 is a critical vulnerability in Linux, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_conntrack_irc: fix parse_dcc() off-by-one OOB read

parse_dcc() treats data_end as an inclusive end pointer, but its only
caller passes data_limit = ib_ptr + datalen, which points one past the
last valid byte.

The newline search loop iterates while tmp <= data_end, so when no
newline is present, *tmp is read at tmp == data_end, one byte beyond
the region filled by skb_header_pointer().

irc_buffer is kmalloc'd as MAX_SEARCH_SIZE + 1 bytes and datalen is
capped at MAX_SEARCH_SIZE, so the stray read does not fault.  The byte
is uninitialized or stale; if it contains an ASCII digit, simple_strtoul
will consume it and produce a wrong DCC IP or port in the conntrack
expectation.  The extra allocation byte is also a fragile guard: if the
cap or allocation size changes, this becomes a real out-of-bounds read.

Change the loop and its post-loop check to use strict less-than,
consistent with the caller's exclusive-end convention.  Update the
function comment accordingly.

## Which versions are affected by CVE-2026-80603?


## How do I fix CVE-2026-80603?

Apply the vendor's patch.

## Is CVE-2026-80603 being exploited?

There is no known exploitation of CVE-2026-80603 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80603 and fix it if it is affected.

What it is: CVE-2026-80603 is a critical vulnerability in Linux, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-80603 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-2026-80603/ (Markdown: https://insights.sbomify.com/CVE-2026-80603/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80603
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80603
- OSV: https://osv.dev/vulnerability/CVE-2026-80603

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80603/
Summaries are generated and may contain mistakes; the official description above is the record.