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CVE-2026-63924
ipv6: exthdrs: refresh nh pointer after ipv6_hop_jumbo()
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem net/ipv6. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-63924 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 | fixed | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
ipv6_hop_jumbo() calls pskb_trim_rcsum(), which can change skb pointers. Let's recompute nh pointer to make sure any change won't mess things up.
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/exthdrs.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on net/ipv6/exthdrs.c · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_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.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_IPV6
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
- 2026-07-19 (3 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.71%, higher than 52.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 2.6.12 | 5.10.259 | b3ac54e5c905 |
| 2.6.12 | 5.15.210 | 645b99b1a185 |
| 2.6.12 | 6.1.176 | 9e883eaa878f |
| 2.6.12 | 6.6.143 | bddaa4dfc7f3 |
| 2.6.12 | 6.12.93 | 72af7beae774 |
| 2.6.12 | 6.18.35 | c512e1c819df |
| 2.6.12 | 7.0.12 | 2b56bbd928c0 |
| 2.6.12 | 7.1 | d47548a36639 |
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
- The bug is in the IPv6 input path (ipv6_rcv → ip6_rcv_core → ipv6_parse_hopopts) triggered by a crafted IPv6 packet with hop-by-hop options containing a Jumbo Payload TLV, reachable from any remote peer that can deliver IPv6 to the host.
- AC:LAttack complexity, low
- An attacker fully controls the crafted IPv6 packet (HBH layout, jumbo length, trailing TLVs) and can send it repeatedly; once the skb is cloned/shared during receive and pskb_trim_rcsum reallocates the head, the stale-pointer UAF is deterministically triggered without races or victim-specific state.
- PR:NPrivileges required, none
- No authentication or local privileges are required; any unauthenticated remote host that can send IPv6 traffic to a listening interface reaches the vulnerable receive handler with no capability or namespace checks along the path.
- UI:NUser interaction, none
- Exploitation requires only delivery of a malicious IPv6 packet and does not depend on any victim user action such as opening files, clicking links, or mounting filesystems.
- S:UScope, unchanged
- Impact is confined to kernel memory corruption and privilege escalation within the same kernel security domain; it does not cross a VM, container, or IOMMU boundary by itself.
- C:HConfidentiality impact, high
- Continued HBH TLV parsing through the stale nh pointer is a use-after-free read of freed skb head memory, which per kernel guidance enables arbitrary kernel memory disclosure when the freed slab is reused.
- I:HIntegrity impact, high
- Stale-pointer UAF during TLV length/type parsing can yield unbounded out-of-bounds reads and corrupt subsequent parsing state, providing memory corruption primitives that can be developed into arbitrary kernel writes or code execution.
- A:HAvailability impact, high
- Dereferencing the freed network-header pointer during TLV parsing can cause immediate kernel oops/panic from invalid memory access, and UAF-triggered parsing errors reliably drop or crash the receive path.