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CVE-2026-64414
netfilter: handle unreadable frags
Published 2026-07-25 (3 months ago) by the Linux kernel CNA. Subsystem net/ipv6. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64414 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixed | 6.12.96-1 | Update the kernel and reboot. Fixed in 6.12.96-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
sashiko reports: When an skb with unreadable fragments (such as from devmem TCP, where skb_frags_readable(skb) returns false) is processed by the u32 module, skb_copy_bits() will safely return a negative error code [..] xt_u32: bail out with hotdrop in this case. gather_frags: return -1, just as if we had no fragment header. nfnetlink_queue: restrict to the linear part. nfnetlink_log: restrict to the linear part. v2: - skb_zerocopy helpers don't copy readable flag, i.e. nfnetlink_queue is broken too xt_u32 shouldn't return true if hotdrop was set.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/ipv6/netfilter/nf_conntrack_reasm.c
net/netfilter/nfnetlink_log.c
net/netfilter/nfnetlink_queue.c
net/netfilter/xt_u32.c
- What this is
- NETFILTERMAINTAINERS section matched on net/*/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nf_defrag_ipv6
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NF_DEFRAG_IPV6' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w nf_defrag_ipv6Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NETFILTER, CONFIG_NF_DEFRAG_IPV6
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-07-25 (3 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.63%, higher than 49.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/ipv6
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.12 | 6.12.96 | 3b13e7635795 |
| 6.12 | 6.18.39 | fc5bfe63bacf |
| 6.12 | 7.1.4 | 57056be3ec12 |
| 6.12 | 7.2 | da5b58478a9c |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- Unreadable skbs arise on the receive side of device-memory TCP, and a remote peer can send packets that traverse netfilter hooks into u32, NFLOG, NFQUEUE, or IPv6 conntrack defragmentation. No local access is required in a network-exposed devmem TCP deployment.
- AC:LAttack complexity, low
- Once devmem/header-split RX and an affected netfilter path are active, a sufficiently long payload or crafted IPv6 extension/fragment layout reliably reaches unreadable fragments. There is no race or condition the attacker must win, and triggering packets can be sent repeatedly.
- PR:NPrivileges required, none
- The triggering packets are processed before application authentication, so the remote peer needs no account or kernel capability. CAP_NET_ADMIN is required for the operator's device and netfilter configuration, not for the attacker sending packets.
- UI:NUser interaction, none
- Packet reception and netfilter processing occur automatically without any victim action after the service and policy are configured.
- S:UScope, unchanged
- The resulting failure affects the same host kernel and does not cross a VM, IOMMU, or other distinct security authority boundary.
- C:NConfidentiality impact, none
- skb_copy_bits() rejects the unreadable fragments before accessing their contents, while the NFQUEUE flag-loss path reaches an invalid page mapping. No attacker-accessible information-disclosure primitive was identified.
- I:NIntegrity impact, none
- The vulnerability causes BUG or invalid-access paths but provides no out-of-bounds write, use-after-free, type confusion, or attacker-controlled data modification.
- A:HAvailability impact, high
- The u32, NFLOG, and IPv6 paths execute BUG(), and the NFQUEUE path can dereference an invalid page during netlink recvmsg. These can produce a kernel oops or panic and can be triggered repeatedly.