# CVE-2026-43501: ipv6: rpl: reserve mac_len headroom when recompressed SRH grows

> A memory corruption vulnerability in the Linux kernel IPv6 RPL implementation allows out-of-bounds writes, potentially leading to code execution or privilege escalation.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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:** 21 May 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-87077, BELL-CVE-2026-43501, DEBIAN-CVE-2026-43501, GHSA-fqx3-r8j8-73qq, ROOT-OS-DEBIAN-11-CVE-2026-43501, ROOT-OS-DEBIAN-12-CVE-2026-43501, ROOT-OS-UBUNTU-2204-CVE-2026-43501, ROOT-OS-UBUNTU-2404-CVE-2026-43501, UBUNTU-CVE-2026-43501

## What is CVE-2026-43501?

CVE-2026-43501 is a critical memory corruption vulnerability in Linux kernel, published on 21 May 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:

ipv6: rpl: reserve mac_len headroom when recompressed SRH grows

ipv6_rpl_srh_rcv() decompresses an RFC 6554 Source Routing Header, swaps
the next segment into ipv6_hdr->daddr, recompresses, then pulls the old
header and pushes the new one plus the IPv6 header back.  The
recompressed header can be larger than the received one when the swap
reduces the common-prefix length the segments share with daddr (CmprI=0,
CmprE>0, seg[0][0] != daddr[0] gives the maximum +8 bytes).

pskb_expand_head() was gated on segments_left == 0, so on earlier
segments the push consumed unchecked headroom.  Once skb_push() leaves
fewer than skb->mac_len bytes in front of data,
skb_mac_header_rebuild()'s call to:

	skb_set_mac_header(skb, -skb->mac_len);

will store (data - head) - mac_len into the u16 mac_header field, which
wraps to ~65530, and the following memmove() writes mac_len bytes ~64KiB
past skb->head.

A single AF_INET6/SOCK_RAW/IPV6_HDRINCL packet over lo with a two
segment type-3 SRH (CmprI=0, CmprE=15) reaches headroom 8 after one
pass; KASAN reports a 14-byte OOB write in ipv6_rthdr_rcv.

Fix this by expanding the head whenever the remaining room is less than
the push size plus mac_len, and request that much extra so the rebuilt
MAC header fits afterwards.

Weakness: CWE-131 (Incorrect Calculation of Buffer Size), CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-43501?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43501?

Apply the vendor's patch.

## Is CVE-2026-43501 being exploited?

There is no known exploitation of CVE-2026-43501 in the wild and no public exploit code.

Public exploit code:

- Termux Privilege Escalation Tool & Root Manager - CVE-2026-43501 (github_poc): https://github.com/Anyone202/cybermeowfia-termux
- https://github.com/ngtuonghung/CVE-2026-43501 (github_poc): https://github.com/ngtuonghung/CVE-2026-43501

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43501 and fix it if it is affected.

What it is: CVE-2026-43501 is a critical memory corruption vulnerability in Linux kernel, published on 21 May 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-2026-43501 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-43501/ (Markdown: https://insights.sbomify.com/CVE-2026-43501/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43501
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43501
- OSV: https://osv.dev/vulnerability/CVE-2026-43501

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43501/
Summaries are generated and may contain mistakes; the official description above is the record.