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VulnerabilityPublished Updated

CVE-2026-43501: Linux kernel · ipv6: rpl: reserve mac_len headroom when recompressed SRH grows

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 9.8 Critical · fixed in c261d07a80576dc8ccf394ef8f074f8c67a06b37 : patch Linux kernel as a priority.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.7% chance of exploitation in 30 days – higher than 54% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers can reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in c261d07a80576dc8ccf394ef8f074f8c67a06b37, be1fa0aa9b4fdd5a8b7a61ba520a690a68391e6e, bde199c72d319a4e207f88daabc888317504e2fb +5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 21 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3, < c261d07a80576dc8ccf394ef8f074f8c67a06b37
Fixed in
  • c261d07a80576dc8ccf394ef8f074f8c67a06b37
LinuxLinuxAffected
  • ≥ 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3, < be1fa0aa9b4fdd5a8b7a61ba520a690a68391e6e
Fixed in
  • be1fa0aa9b4fdd5a8b7a61ba520a690a68391e6e
LinuxLinuxAffected
  • ≥ 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3, < bde199c72d319a4e207f88daabc888317504e2fb
Fixed in
  • bde199c72d319a4e207f88daabc888317504e2fb
LinuxLinuxAffected
  • ≥ 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3, < 7398ebefbfd4f8a31d4f665a4213302fa995494b
Fixed in
  • 7398ebefbfd4f8a31d4f665a4213302fa995494b
LinuxLinuxAffected
  • ≥ 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3, < 9e6bf146b55999a095bb14f73a843942456d1adc
Fixed in
  • 9e6bf146b55999a095bb14f73a843942456d1adc
LinuxLinuxAffected
  • ≥ 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3, < 8e8be63465a5e80394c70324603dfea1bfdad48f
Fixed in
  • 8e8be63465a5e80394c70324603dfea1bfdad48f

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.

References

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