# CVE-2026-99042: io_uring/net: populate CONNECT filter fields for 24-byte sockaddr_in6


- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 24 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-99042, GHSA-cg89-27g3-43v4, UBUNTU-CVE-2026-99042

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99042 and fix it if it is affected.

What it is: CVE-2026-99042 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99042 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-2026-99042/ (Markdown: https://insights.sbomify.com/CVE-2026-99042/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99042
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99042
- OSV: https://osv.dev/vulnerability/CVE-2026-99042

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99042/
Summaries are generated and may contain mistakes; the official description above is the record.