# CVE-2026-68118: tcp: challenge ACK for non-exact RST in SYN-RECEIVED

> Attackers can disrupt TCP connections by sending non-exact RST packets, causing the kernel to drop requests instead of sending challenge ACKs.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-95003, BELL-CVE-2026-68118, DEBIAN-CVE-2026-68118, GHSA-wr69-pfwc-72wx, UBUNTU-CVE-2026-68118

## What is CVE-2026-68118?

CVE-2026-68118 is a high-severity denial of service vulnerability in Linux, published on 10 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:

tcp: challenge ACK for non-exact RST in SYN-RECEIVED

The SYN-RECEIVED request-socket path in tcp_check_req() accepts an
in-window RST without requiring SEG.SEQ to exactly match RCV.NXT.  A
non-exact RST therefore removes the request instead of eliciting a
challenge ACK.

RFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in
SYN-RECEIVED: an exact RST resets the connection, while a non-exact
in-window RST must trigger a challenge ACK and be dropped.

Apply that check before the ACK-field validation, following the RFC
sequence-number, RST, then ACK processing order.  Factor the per-netns
challenge ACK quota out of tcp_send_challenge_ack() so request sockets
can share it.  Use the request socket's send_ack() callback and its own
out-of-window ACK timestamp to send and rate-limit the response.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-68118?


## How do I fix CVE-2026-68118?

Apply the vendor's patch.

## Is CVE-2026-68118 being exploited?

There is no known exploitation of CVE-2026-68118 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68118 and fix it if it is affected.

What it is: CVE-2026-68118 is a high-severity denial of service vulnerability in Linux, published on 10 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-2026-68118 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-2026-68118/ (Markdown: https://insights.sbomify.com/CVE-2026-68118/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68118
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68118
- OSV: https://osv.dev/vulnerability/CVE-2026-68118

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68118/
Summaries are generated and may contain mistakes; the official description above is the record.