xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path

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Summary

CVECVE-2026-45905
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-27 14:17:04 UTC
Updated2026-05-27 14:48:31 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path icmp_route_lookup() performs multiple route lookups to find a suitable route for sending ICMP error messages, with special handling for XFRM (IPsec) policies. The lookup sequence is: 1. First, lookup output route for ICMP reply (dst = original src) 2. Pass through xfrm_lookup() for policy check 3. If blocked (-EPERM) or dst is not local, enter "reverse path" 4. In reverse path, call xfrm_decode_session_reverse() to get fl4_dec which reverses the original packet's flow (saddr<->daddr swapped) 5. If fl4_dec.saddr is local (we are the original destination), use __ip_route_output_key() for output route lookup 6. If fl4_dec.saddr is NOT local (we are a forwarding node), use ip_route_input() to simulate the reverse packet's input path 7. Finally, pass rt2 through xfrm_lookup() with XFRM_LOOKUP_ICMP flag The bug occurs in step 6: ip_route_input() is called with fl4_dec.daddr (original packet's source) as destination. If this address becomes local between the initial check and ip_route_input() call (e.g., due to concurrent "ip addr add"), ip_route_input() returns a LOCAL route with dst.output set to ip_rt_bug. This route is then used for ICMP output, causing dst_output() to call ip_rt_bug(), triggering a WARN_ON: ------------[ cut here ]------------ WARNING: net/ipv4/route.c:1275 at ip_rt_bug+0x21/0x30, CPU#1 Call Trace: <TASK> ip_push_pending_frames+0x202/0x240 icmp_push_reply+0x30d/0x430 __icmp_send+0x1149/0x24f0 ip_options_compile+0xa2/0xd0 ip_rcv_finish_core+0x829/0x1950 ip_rcv+0x2d7/0x420 __netif_receive_skb_one_core+0x185/0x1f0 netif_receive_skb+0x90/0x450 tun_get_user+0x3413/0x3fb0 tun_chr_write_iter+0xe4/0x220 ... Fix this by checking rt2->rt_type after ip_route_input(). If it's RTN_LOCAL, the route cannot be used for output, so treat it as an error. The reproducer requires kernel modification to widen the race window, making it unsuitable as a selftest. It is available at: https://gist.github.com/mrpre/eae853b72ac6a750f5d45d64ddac1e81

Risk And Classification

EPSS: 0.000240000 probability, percentile 0.073930000 (date 2026-05-29)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 9a95ec9144eeff1fc6fbcc21b677e322c6f1430b git Not specified
CNA Linux Linux affected 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 2c1f59005da9dd4b07b26984fd719e36557dc57c git Not specified
CNA Linux Linux affected 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 b04061f89ffc6168e7ec3c71d0086ec3c3797228 git Not specified
CNA Linux Linux affected 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 1c9ef28f643cce34a6a6c36c8f4d6d60a60db7e1 git Not specified
CNA Linux Linux affected 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 423ce12d10b426709489d6b84fdaa6d2f31c5652 git Not specified
CNA Linux Linux affected 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 81b84de32bb27ae1ae2eb9acf0420e9d0d14bf00 git Not specified
CNA Linux Linux affected 2.6.25 Not specified
CNA Linux Linux unaffected 2.6.25 semver Not specified
CNA Linux Linux unaffected 6.1.165 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.128 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.75 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.14 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.4 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/9a95ec9144eeff1fc6fbcc21b677e322c6f1430b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/423ce12d10b426709489d6b84fdaa6d2f31c5652 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/81b84de32bb27ae1ae2eb9acf0420e9d0d14bf00 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/2c1f59005da9dd4b07b26984fd719e36557dc57c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b04061f89ffc6168e7ec3c71d0086ec3c3797228 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1c9ef28f643cce34a6a6c36c8f4d6d60a60db7e1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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