CVE-2026-43501

ipv6: rpl: reserve mac_len headroom when recompressed SRH grows

Published May 21, 2026 CVSS 3.1 · 9.8 Critical EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4664-1 linux security update
Debian DLA Debian DLA DLA-4665-1 linux security update
Debian DLA Debian DLA DLA-4671-1 linux-6.1 security update
Ubuntu USN Ubuntu USN USN-8488-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8489-1 Linux kernel (OEM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8490-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8491-1 Linux kernel (OEM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8492-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8493-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8488-2 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-8492-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8493-2 Linux kernel (Oracle) vulnerabilities
Ubuntu USN Ubuntu USN USN-8497-1 Linux kernel (Low Latency) vulnerabilities
Ubuntu USN Ubuntu USN USN-8498-1 Linux kernel (NVIDIA Tegra) vulnerabilities
Ubuntu USN Ubuntu USN USN-8499-1 Linux kernel (Xilinx) vulnerabilities
Ubuntu USN Ubuntu USN USN-8507-1 Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN Ubuntu USN USN-8508-1 Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN Ubuntu USN USN-8492-3 Linux kernel (Raspberry Pi Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-8490-2 Linux kernel (Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-8492-4 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-8492-5 Linux kernel (FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8527-1 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-8528-1 Linux kernel (Xilinx ZynqMP) vulnerabilities
Ubuntu USN Ubuntu USN USN-8545-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-8546-1 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-8547-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8569-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-8603-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8604-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8605-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8606-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8607-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8609-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8547-2 Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8619-1 Linux kernel (HWE) vulnerabilities
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Weaknesses CWE-119
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}

Type Values Removed Values Added
Weaknesses CWE-131
References
Metrics threat_severity

None

cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Important

Type Values Removed Values Added
Weaknesses CWE-119
Type Values Removed Values Added
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.
Title ipv6: rpl: reserve mac_len headroom when recompressed SRH grows
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Nov 10, 2026, 12:46 PM
Reserved
May 1, 2026, 2:12 PM
Status
Modified
Published
May 21, 2026, 1:16 PM
Modified
Nov 10, 2026, 1:19 PM
Severity
Important
Public date
May 21, 2026, 12:00 AM