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CVE-2026-63922
ipv6: exthdrs: refresh nh after handling HAO option
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-2026-63922 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
ip6_parse_tlv() caches skb_network_header(skb) in nh while walking IPv6 TLVs. ipv6_dest_hao() may call pskb_expand_head() for a cloned skb, which can move the skb head and invalidate the cached network header pointer. Refresh nh after ipv6_dest_hao() returns so any trailing padding or TLVs are parsed from the current skb head. This matches the existing pattern used in ip6_parse_tlv() after helpers that can modify skb header storage.
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 |
|---|---|---|
| 2.6.19 | 5.10.259 | b3ac54e5c905 |
| 2.6.19 | 5.15.210 | f8aabed3ff3e |
| 2.6.19 | 6.1.176 | 1a11eb7431e3 |
| 2.6.19 | 6.6.143 | 12d957979e4a |
| 2.6.19 | 6.12.93 | ff375ed1cba8 |
| 2.6.19 | 6.18.35 | 751db1b802a0 |
| 2.6.19 | 7.0.12 | 9b6dcc0a39fd |
| 2.6.19 | 7.1 | f7b52afe3592 |
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 reached on the standard IPv6 input path (ipv6_rcv → ip6_input → ip6_protocol_deliver_rcu → ipv6_destopt_rcv) when a remotely sent IPv6 packet carries a Destination Options header processed by ip6_parse_tlv().
- AC:LAttack complexity, low
- The attacker fully controls the crafted IPv6 Destination Options layout (HAO TLV followed by trailing TLVs/padding); once CONFIG_IPV6_MIP6 and matching XFRM state exist on the target, triggering the stale-pointer condition is a reliable single-packet attack without races or victim-specific timing.
- PR:NPrivileges required, none
- No local privileges or authentication are required; any remote host that can deliver IPv6 traffic to a listening interface can reach this pre-authentication receive-path parser (destopt_protocol uses INET6_PROTO_NOPOLICY).
- UI:NUser interaction, none
- Exploitation requires only sending a malicious IPv6 packet; no victim interaction such as opening files, clicking links, or mounting filesystems is needed.
- S:UScope, unchanged
- Impact is confined to kernel memory corruption and privilege escalation within the kernel’s security authority; it does not cross VM, container, or IOMMU boundaries.
- C:HConfidentiality impact, high
- After pskb_expand_head() frees the old skb head, ip6_parse_tlv() continues parsing trailing TLVs through the stale nh pointer, causing out-of-bounds/use-after-free reads of kernel heap memory that can disclose sensitive kernel data.
- I:HIntegrity impact, high
- Use-after-free of the skb head buffer during TLV parsing is heap memory corruption that can be leveraged for arbitrary kernel writes and control-flow hijacking, not merely a bounded parse error.
- A:HAvailability impact, high
- Reading through the stale network-header pointer into freed or invalid memory can cause kernel oops/panic or unrecoverable instability, satisfying high availability impact even before full exploitation.