CVE-2026-43501: Linux kernel · ipv6: rpl: reserve mac_len headroom when recompressed SRH grows
Affects Linux kernelSource CVE Database V5
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
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 21 May 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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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
- git.kernel.org/stable/c/bde199c72d319a4e207f88daabc888317504e2fb (opens in a new tab)
- git.kernel.org/stable/c/be1fa0aa9b4fdd5a8b7a61ba520a690a68391e6e (opens in a new tab)
- git.kernel.org/stable/c/0a9e8053f1f8a8e1bfc1dd61ffe67be6c1180402 (opens in a new tab)
- git.kernel.org/stable/c/8e8be63465a5e80394c70324603dfea1bfdad48f (opens in a new tab)
- git.kernel.org/stable/c/4babc2d9fda2df43823b85d08a0180b68f1b0854 (opens in a new tab)
- git.kernel.org/stable/c/c261d07a80576dc8ccf394ef8f074f8c67a06b37 (opens in a new tab)
- git.kernel.org/stable/c/7398ebefbfd4f8a31d4f665a4213302fa995494b (opens in a new tab)
- git.kernel.org/stable/c/9e6bf146b55999a095bb14f73a843942456d1adc (opens in a new tab)
- access.redhat.com/security/cve/CVE-2026-43501 (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2480457 (opens in a new tab)
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-43501.json (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:27731 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:25191 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:34095 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:27713 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:34094 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:25217 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:33900 (opens in a new tab)
- cert-portal.siemens.com/productcert/html/ssa-019113.html (opens in a new tab)
- cert-portal.siemens.com/productcert/html/ssa-457936.html (opens in a new tab)