Copyright © 2012 Red Hat, Inc. All rights reserved. Important 2026-05-21T00:00:00 kernel: ipv6: rpl: reserve mac_len headroom when recompressed SRH grows 7.5 CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H CWE-131

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.

A flaw was found in the Linux kernel. A local attacker can exploit an out-of-bounds write vulnerability when the kernel recomputes an IPv6 Source Routing Header (SRH). This issue occurs because insufficient headroom is reserved during the recompression process, leading to memory corruption. Successful exploitation could result in a denial of service or potentially arbitrary code execution.

This is an Important flaw. A local attacker can exploit an out-of-bounds write in the Linux kernel's IPv6 Source Routing Header (SRH) recompression, which could lead to a denial of service or arbitrary code execution. This vulnerability impacts Red Hat Enterprise Linux 9 and 10, and Red Hat In-Vehicle OS 2, due to insufficient memory handling during SRH processing. To mitigate this issue, disable IPv6 Source Routing by setting the `accept_source_route` sysctl parameter to 0 for all IPv6 interfaces. This can prevent the kernel from processing IPv6 Source Routing Headers, thereby avoiding the vulnerable code path. To disable IPv6 Source Routing: `sysctl -w net.ipv6.conf.all.accept_source_route=0` `sysctl -w net.ipv6.conf.default.accept_source_route=0` To make this change persistent across reboots, add the following lines to `/etc/sysctl.d/99-disable-ipv6-srh.conf`: `net.ipv6.conf.all.accept_source_route = 0` `net.ipv6.conf.default.accept_source_route = 0` Then, apply the changes with: `sysctl --system` Disabling IPv6 Source Routing may impact network configurations that rely on this feature. Red Hat Enterprise Linux 10 Affected kernel Red Hat Enterprise Linux 6 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel-rt Red Hat Enterprise Linux 8 Not affected kernel Red Hat Enterprise Linux 8 Not affected kernel-rt Red Hat Enterprise Linux 9 Affected kernel Red Hat Enterprise Linux 9 Affected kernel-rt https://www.cve.org/CVERecord?id=CVE-2026-43501 https://nvd.nist.gov/vuln/detail/CVE-2026-43501 https://lore.kernel.org/linux-cve-announce/2026052159-CVE-2026-43501-63a6@gregkh/T