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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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.
Sources
Also known as BELL-CVE-2026-80603, DEBIAN-CVE-2026-80603, GHSA-66q8-v4rr-393c, UBUNTU-CVE-2026-80603.