CVE-2026-99042 io_uring/net: populate CONNECT filter fields for 24-byte sockaddr_in6
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-99042?
CVE-2026-99042 is a high-severity vulnerability in Linux, published on 23 Oct 2026.
Official description
In the Linux kernel, the following vulnerability has been resolved:
io_uring/net: populate CONNECT filter fields for 24-byte sockaddr_in6
io_connect_bpf_populate() fills connect.port and connect.v6_addr for AF_INET6 only when addr_len >= sizeof(struct sockaddr_in6), i.e. 28 bytes.
The IPv6 connect paths accept SIN6_LEN_RFC2133 (24 bytes), which already holds sin6_port and sin6_addr. io_connect() passes addr_len to the socket layer unchanged.
At addr_len 24 the filter sees family AF_INET6 with port and address zero, while the kernel connects to the real destination. A filter that denies an IPv6 port or address is bypassed. Denying connect.port == P rejects [::1]:P with -EACCES at addr_len 28 but connects at addr_len 24.
Use SIN6_LEN_RFC2133 as the threshold. sin6_scope_id stays zero when absent.
The threshold mismatch was found by an AI coding assistant (Claude Code) comparing this hook against the net/ipv6 length checks on my instructions; it also drafted the reproducer and this patch. I verified the bypass and the fix in a VM on 7.3-rc6 and that 7.2 has the same code.
Which versions are affected by CVE-2026-99042?
How do I fix CVE-2026-99042?
Upgrade to a fixed version.
Is CVE-2026-99042 being exploited?
There is no known exploitation of CVE-2026-99042 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-99042, GHSA-cg89-27g3-43v4, UBUNTU-CVE-2026-99042.