CVE-2026-43501
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk38th percentile — higher than 38% of all known CVEs
Summary
A vulnerability was found in the Linux kernel's ipv6_rpl_srh_rcv() function handling the RPL Source Routing Header (RFC 6554). During decompression and recompression of the SRH, the header may grow, and insufficient headroom checking leads to an out-of-bounds write.
Risk Assessment
An attacker can send a crafted IPv6 packet with an SRH header, potentially causing kernel memory corruption, which may lead to privilege escalation or denial of service (DoS).
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit ensuring proper headroom expansion before the push operation).
Original NVD description (English source)
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.