# CVE-2026-98372: xfrm: iptfs: fix stack OOB read in iptfs_skb_reset_frag_walk()

> A remote attacker can trigger a stack out-of-bounds read in the Linux kernel's IP-TFS implementation via crafted packets, potentially causing a crash or leaking memory.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-98372, DEBIAN-CVE-2026-98372, GHSA-9gpc-jg89-88qg, UBUNTU-CVE-2026-98372

## What is CVE-2026-98372?

CVE-2026-98372 is a memory corruption vulnerability in Linux, published on 6 Oct 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:

xfrm: iptfs: fix stack OOB read in iptfs_skb_reset_frag_walk()

iptfs_skb_reset_frag_walk() advances to the fragment containing @offset
with an unbounded loop:

	while (offset >= walk->past + walk->frags[walk->fragi].len)
		walk->past += walk->frags[walk->fragi++].len;

walk->fragi is advanced and walk->frags[walk->fragi] is dereferenced
without ever checking fragi against walk->nr_frags. When the requested
offset is at or beyond the total length spanned by the walk's fragments,
fragi runs past nr_frags and off the end of the fixed-size on-stack
frags[MAX_SKB_FRAGS + 1] array, reading out-of-bounds stack memory.

The two callers behave differently: iptfs_skb_add_frags() already guards
against this with

	if (!walk->nr_frags ||
	    offset >= walk->total + walk->initial_offset)
		return len;

but iptfs_skb_can_add_frags() has no such guard and calls
iptfs_skb_reset_frag_walk() unconditionally, so it performs the
out-of-range walk. Its own "fragi < walk->nr_frags" bound check runs only
afterwards, too late to prevent the read.

This is reachable from the receive path: a crafted IP-TFS (AGGFRAG)
payload delivered to an IPTFS SA drives iptfs_reassem_cont() ->
iptfs_skb_can_add_frags() with an offset past the fragment total, e.g.:

  BUG: KASAN: stack-out-of-bounds in iptfs_skb_reset_frag_walk+0x235/0x250
  Read of size 4 at addr ffff888008ad7210 by task repro/345
   iptfs_skb_reset_frag_walk+0x235/0x250 net/xfrm/xfrm_iptfs.c:392
   iptfs_skb_can_add_frags+0x155/0x310  net/xfrm/xfrm_iptfs.c:420
   iptfs_reassem_cont+0xcf8/0x1140      net/xfrm/xfrm_iptfs.c:902
   iptfs_input_ordered+0x552/0x670      net/xfrm/xfrm_iptfs.c:1280
   iptfs_input+0x3d6/0xde0              net/xfrm/xfrm_iptfs.c:1741
   xfrm_input+0x282f/0x6140             net/xfrm/xfrm_input.c:700
   xfrm4_esp_rcv+0x93/0x120             net/ipv4/xfrm4_protocol.c:104
   ip_rcv+0x278/0x2d0                   net/ipv4/ip_input.c:612

Give iptfs_skb_can_add_frags() the same up-front guard that
iptfs_skb_add_frags() already has, so the walk is never entered with an
out-of-range offset. When it triggers, the caller falls back to the
existing linearize-and-copy path, which is safe.

## Which versions are affected by CVE-2026-98372?


## How do I fix CVE-2026-98372?

Apply the vendor's patch.

## Is CVE-2026-98372 being exploited?

There is no known exploitation of CVE-2026-98372 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98372 and fix it if it is affected.

What it is: CVE-2026-98372 is a memory corruption vulnerability in Linux, published on 6 Oct 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-2026-98372 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-2026-98372/ (Markdown: https://insights.sbomify.com/CVE-2026-98372/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98372
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98372
- OSV: https://osv.dev/vulnerability/CVE-2026-98372

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98372/
Summaries are generated and may contain mistakes; the official description above is the record.