CVE-2026-43501
Received Received - Intake
Linux Kernel IPv6 RPL SRH Headroom Buffer Overflow

Publication date: 2026-05-21

Last updated on: 2026-05-21

Assigner: kernel.org

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.
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Meta Information
Published
2026-05-21
Last Modified
2026-05-21
Generated
2026-05-21
AI Q&A
2026-05-21
EPSS Evaluated
N/A
NVD
CVE-2026-43501
EUVD
EUVD-2026-31276
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
Helpful Resources
Exploitability
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KEV
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CWE ID Description
CWE-UNKNOWN
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AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability exists in the Linux kernel's handling of IPv6 source routing headers (SRH). Specifically, the function ipv6_rpl_srh_rcv() decompresses an RFC 6554 Source Routing Header, swaps the next segment into the IPv6 destination address, recompresses the header, and then replaces the old header with the new one plus the IPv6 header. However, when the recompressed header grows larger than the original due to changes in segment prefix lengths, the kernel does not properly reserve enough headroom in the packet buffer.

Because of insufficient headroom reservation, a subsequent operation (skb_set_mac_header) writes data beyond the allocated buffer boundary (out-of-bounds write), potentially corrupting memory. This can happen when processing certain IPv6 packets with specific source routing headers, leading to a memory corruption issue detected by KASAN (Kernel Address Sanitizer).

The fix involves expanding the buffer headroom whenever the remaining space is less than the size needed for the push operation plus the MAC header length, ensuring safe memory operations.


How can this vulnerability impact me? :

This vulnerability can lead to out-of-bounds memory writes in the Linux kernel when processing specially crafted IPv6 packets with source routing headers. Such memory corruption can cause system instability, crashes, or potentially allow an attacker to execute arbitrary code with kernel privileges.

Because the issue occurs in the kernel's network stack, it could be exploited remotely by sending malicious IPv6 packets, especially on systems that accept raw IPv6 packets or use source routing features.


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