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CVE-2026-43501

Linux: ipv6: rpl: reserve mac_len headroom when recompressed SRH grows

Linux LinuxOperating systems
Open in ThreatlineRecord JSON
CVSS
9.8Critical
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.73%Chance of exploitation activity in the next 30 days, higher than 54% of CVEs. Scored 25 Oct 2026FIRST EPSS
Fixed in0a9e8053f1f8a8e1bfc1dd61ffe67be6c1180402Also 8e8be63465a5e80394c70324603dfea1bfdad48f, 4babc2d9fda2df43823b85d08a0180b68f1b0854 and 2 moreCVE List
Published21 May 2026Updated 19 Oct 2026CVE List

What fixes it

  • 0a9e8053f1f8a8e1bfc1dd61ffe67be6c1180402LinuxCVE List
  • 8e8be63465a5e80394c70324603dfea1bfdad48fLinuxCVE List
  • 4babc2d9fda2df43823b85d08a0180b68f1b0854LinuxCVE List
  • 7398ebefbfd4f8a31d4f665a4213302fa995494bLinuxCVE List
  • 9e6bf146b55999a095bb14f73a843942456d1adcLinuxCVE List

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Timeline

  1. 21 May 2026, 12:17 UTCPublishedCVE List
  2. 26 Oct 2026, 00:05 UTCExploit code publicBluesky: CVE posts

Reports 1

1 outlet mention it. Reports are not confirmation; each links to its source.

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.

Text from CVE List

Affected versions 18

  • Linuxaffected: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 before bde199c72d319a4e207f88daabc888317504e2fbCVE List
  • Linuxaffected: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 before be1fa0aa9b4fdd5a8b7a61ba520a690a68391e6eCVE List
  • Linuxaffected: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 before 0a9e8053f1f8a8e1bfc1dd61ffe67be6c1180402CVE List
  • Linuxaffected: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 before 8e8be63465a5e80394c70324603dfea1bfdad48fCVE List
  • Linuxaffected: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 before 4babc2d9fda2df43823b85d08a0180b68f1b0854CVE List
  • Linuxaffected: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 before c261d07a80576dc8ccf394ef8f074f8c67a06b37CVE List
  • Linuxaffected: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 before 7398ebefbfd4f8a31d4f665a4213302fa995494bCVE List
  • Linuxaffected: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 before 9e6bf146b55999a095bb14f73a843942456d1adcCVE List
  • Linuxaffected: 5.7CVE List
  • Linuxunaffected: all versions before 5.7CVE List
  • Linuxunaffected: 5.10.258 through 5.10.*CVE List
  • Linuxunaffected: 5.15.209 through 5.15.*CVE List
  • Linuxunaffected: 6.1.175 through 6.1.*CVE List
  • Linuxunaffected: 6.6.140 through 6.6.*CVE List
  • Linuxunaffected: 6.12.86 through 6.12.*CVE List
  • Linuxunaffected: 6.18.27 through 6.18.*CVE List
  • Linuxunaffected: 7.0.4 through 7.0.*CVE List
  • Linuxunaffected: 7.1CVE List

References 20