# CVE-2026-72408: geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint

> An attacker can trigger an out-of-bounds read in the Linux kernel Geneve driver by sending crafted packets, potentially causing a crash or information disclosure.

- **Severity:** Critical 10.0 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/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:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-72408, GHSA-p4xr-mfr6-cf8x, UBUNTU-CVE-2026-72408

## What is CVE-2026-72408?

CVE-2026-72408 is a critical memory corruption vulnerability in Linux, published on 15 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:

geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint

geneve_gro_receive() reads the GRO hint through geneve_sk_gro_hint_off(),
which honours it only when the socket enabled IFLA_GENEVE_GRO_HINT
(gs->gro_hint). geneve_gro_complete() instead calls the low-level
geneve_opt_gro_hint_off() and acts on the hint unconditionally.

On a tunnel without the hint, receive aggregates the frames as plain
ETH_P_TEB while complete still honours an attacker-supplied hint option: it
inflates gh_len by gro_hint->nested_hdr_len (u8) and redirects the dispatch
type, so the inner gro_complete handler runs at nhoff + gh_len, an offset
receive never pulled nor validated, reading out of bounds of the skb head:

  BUG: KASAN: slab-out-of-bounds in ipv6_gro_complete (net/ipv6/ip6_offload.c:196)
  Read of size 1 at addr ffff88800fe91980 by task exploit/153
   ipv6_gro_complete (net/ipv6/ip6_offload.c:196)
   geneve_gro_complete (drivers/net/geneve.c:965)
   udp_gro_complete (net/ipv4/udp_offload.c:940)
   inet_gro_complete (net/ipv4/af_inet.c:1621)
   __gro_flush (net/core/gro.c:306)

Gate the complete path on gs->gro_hint too via geneve_sk_gro_hint_off(), so
both paths agree. Tunnels that enable the hint are unaffected.

## Which versions are affected by CVE-2026-72408?


## How do I fix CVE-2026-72408?

Apply the vendor's patch.

## Is CVE-2026-72408 being exploited?

There is no known exploitation of CVE-2026-72408 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72408 and fix it if it is affected.

What it is: CVE-2026-72408 is a critical memory corruption vulnerability in Linux, published on 15 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-2026-72408 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-2026-72408/ (Markdown: https://insights.sbomify.com/CVE-2026-72408/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72408
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72408
- OSV: https://osv.dev/vulnerability/CVE-2026-72408

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72408/
Summaries are generated and may contain mistakes; the official description above is the record.