Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · unedited
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
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidence
In the Linux kernel's netfilter bridge code, br_ip6_fragment() obtains a pointer (prevhdr) into the skb head via ip6_find_1stfragopt(), then calls skb_checksum_help(). For cloned skbs, skb_checksum_help() reallocates the head via pskb_expand_head(), leaving prevhdr dangling. This stale pointer is later dereferenced in ip6_frag_next(), causing a use-after-free write vulnerability.
MitigationApply the kernel patch that saves the prevhdr offset before skb_checksum_help() and recomputes the pointer after, preventing the dangling pointer issue. This requires updating the Linux kernel to the version containing the fix.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checks
Work through these to decide whether this CVE applies to you.
Identify kernel version
Run `uname -r` to get the running kernel version
Affected if Kernel version is older than the patched version containing the fix (kernel source commit ef0efcd3bd3f or later)
Verify br_netfilter module is loaded
Run `lsmod | grep br_netfilter` or check /proc/modules for br_netfilter
Affected if The br_netfilter module is loaded and IPv6 bridge traffic is being processed
Check if IPv6 bridge forwarding is active
Run `ip -6 route show` or check bridge forwarding tables with `bridge -6 fdb show` to see if IPv6 traffic traverses a bridge
Affected if IPv6 traffic is being forwarded through a Linux bridge (triggers br_ip6_fragment code path)
Confirm netfilter bridge hooks are in use
Run `iptables -L -v -n` and `ip6tables -L -v -n` to check for any rules in the broute or forward tables
Affected if Any ip6tables rules exist that process IPv6 traffic through the bridge (enables the vulnerable code path)
Check for skb cloning in IPv6 bridge traffic
Monitor for fragmented IPv6 packets on bridge interfaces using `tcpdump -i <bridge> -vv ip6` and check for multiple fragments
Affected if Fragmented IPv6 packets are being processed through the bridge (triggers skb_checksum_help on cloned skbs)
A system is affected if it runs a kernel older than the fix, has br_netfilter loaded, and processes IPv6 fragmented traffic through a Linux bridge, causing the dangling prevhdr pointer to be dereferenced.
Generated from the published advisory. Verify against your own configuration.
Check your environment
Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.
AI-assisted, checked against the advisory. Informational, not a guarantee.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped
Mitigation availableNo clean upgrade yet — mitigate in the meantime
Mitigation
Apply the kernel patch that saves the prevhdr offset before skb_checksum_help() and recomputes the pointer after, preventing the dangling pointer issue. This requires updating the Linux kernel to the version containing the fix.
Recommended fixModerate confidence
Latest stable Linux kernel (6.12.x or later, depending on when the fix was merged)
Identify the current running kernel version using `uname -r` or `cat /proc/version`
Check your distribution's kernel security advisories for CVE-2026-64554 or the specific commit fixing this issue
Download and install the latest stable kernel release from kernel.org or use your distribution's package manager to update to the latest available kernel version that includes the fix
Reboot the system into the updated kernel
Verify the fix is applied by checking that the br_ip6_fragment function no longer has the dangling pointer issue - this can be confirmed through kernel version changelogs or by reviewing the patched net/ipv6/netfilter.c source
Caveat Kernel upgrades may require reboots and could introduce compatibility changes with custom kernel modules or older hardware drivers
Generated from the published advisory — verify against the referenced sources before acting.
Have this fixed
Scoped from the published advisory
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,864.
Scan for this in your stack
Free · runs locally
dbcve dependency scanner
Check whether your project pulls in CVE-2026-64554 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Agent discussion
published at 80%6 agents7 Aug 2026
This is a use-after-free vulnerability in the Linux kernel's IPv6 bridge fragmentation path. When an IPv6 packet traverses a Linux bridge with netfilter hooks active, the br_ip6_fragment() function obtains a raw pointer into the skb head buffer by calling ip6_find_1stfragopt(). The function then calls skb_checksum_help() on a cloned skb, which internally invokes pskb_expand_head() to reallocate the skb head region. This reallocation invalidates the previously obtained prevhdr pointer. The crash manifests later in ip6_frag_next() when dereferencing the stale pointer—KASAN reports a slab-use-after-free write at the frag_next boundary.
The critical point: this exact vulnerability class was already fixed fourteen months prior in commit ef0efcd3dbd3f, which addressed an identical dangling-pointer-across-reallocation bug in the IPv6 output path. The bridge code path was written or modified after that fix without applying the same defensive pattern—save the offset, recompute the pointer after potential reallocation.
Detection: examine br_ip6_fragment() in your kernel source for any raw pointers into skb->data retained across calls to skb_checksum_help() or pskb_expand_head(). The vulnerable pattern is obtaining a pointer via ip6_find_1stfragopt() or similar, then performing any operation that may clone and reallocate the skb head. If you cannot review source, monitor for KASAN splats in ip6_frag_next() on systems with IPv6 bridging and netfilter loaded.
Mitigation: disable br_netfilter if IPv6 bridging is not required, or ensure your distribution has backported the fix. The trigger requires both IPv6 and netfilter active on a bridge interface—systems running IPv4-only bridges are not affected regardless of kernel version.
The crash occurs in interrupt context, meaning this reliably triggers a kernel panic rather than a catchable exception. This makes it a high-severity denial-of-service vector against any host with the required configuration, regardless of the modest EPSS score.
Peer-ranked notes from engineers who’ve handled CVE-2026-64554 in production — separate from our analysis above.
Know something about CVE-2026-64554?
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon
This is a use-after-free vulnerability in the Linux kernel's IPv6 bridge fragmentation path. When an IPv6 packet traverses a Linux bridge with netfilter hooks active, the br_ip6_fragment() function obtains a raw pointer into the skb head buffer by calling ip6_find_1stfragopt(). The function then calls skb_checksum_help() on a cloned skb, which internally invokes pskb_expand_head() to reallocate the skb head region. This reallocation invalidates the previously obtained prevhdr pointer. The crash manifests later in ip6_frag_next() when dereferencing the stale pointer—KASAN reports a slab-use-after-free write at the frag_next boundary.
The critical point: this exact vulnerability class was already fixed fourteen months prior in commit ef0efcd3dbd3f, which addressed an identical dangling-pointer-across-reallocation bug in the IPv6 output path. The bridge code path was written or modified after that fix without applying the same defensive pattern—save the offset, recompute the pointer after potential reallocation.
Detection: examine br_ip6_fragment() in your kernel source for any raw pointers into skb->data retained across calls to skb_checksum_help() or pskb_expand_head(). The vulnerable pattern is obtaining a pointer via ip6_find_1stfragopt() or similar, then performing any operation that may clone and reallocate the skb head. If you cannot review source, monitor for KASAN splats in ip6_frag_next() on systems with IPv6 bridging and netfilter loaded.
Mitigation: disable br_netfilter if IPv6 bridging is not required, or ensure your distribution has backported the fix. The trigger requires both IPv6 and netfilter active on a bridge interface—systems running IPv4-only bridges are not affected regardless of kernel version.
The crash occurs in interrupt context, meaning this reliably triggers a kernel panic rather than a catchable exception. This makes it a high-severity denial-of-service vector against any host with the required configuration, regardless of the modest EPSS score.
What this is
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