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CVE-2026-74598
ipv6: fix Route Information option length validation
Published 2026-08-22 (2 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-2026-74598 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 | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
rt6_route_rcv() validates the Route Information option (RFC 4191) length against the prefix length, but both checks are off by one. rinfo->length is the ND option length in units of 8 octets and it *includes* the 8-byte option header, so an option carrying N bytes of prefix has length == 1 + N/8. RFC 4191 section 2.3 requires length 3 when Prefix Length is greater than 64, and 2 or 3 when it is greater than 0. The code accepts length >= 2 and length >= 1 respectively. ipv6_addr_prefix() then copies prefix_len/8 bytes out of rinfo->prefix, so a Router Advertisement with (prefix_len=128, length=2) or (prefix_len=64, length=1) makes the kernel read up to 8 bytes past the end of the option. Those bytes end up in the prefix of the route that gets installed, so they are visible to userspace: # RA with a Route Information option (prefix_len=128, length=2) # followed by a source link-layer address option, 01 01 de ad be ef ca fe $ ip -6 route show 2001:db8:dead:beef:101:dead:beef:cafe via fe80::1234 dev veth0 proto ra ^^^^^^^^^^^^^^^^^^ the next option, read out of bounds When the Route Information option is the last one in the packet, those eight bytes come from the skb tail room instead. Reject the option lengths RFC 4191 does not allow.
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/route.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on net/ipv6/route.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, sid, bookworm · linux-6.12y
- 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
- 2026-08-22 (2 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Nsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.43%, higher than 35.3% 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 |
|---|---|---|
| 2.6.17 | 5.10.265 | 2f6f94eda124 |
| 2.6.17 | 5.15.216 | 7eac87396c44 |
| 2.6.17 | 6.1.183 | 7309529f257a |
| 2.6.17 | 6.6.152 | 0b9e02f3bd31 |
| 2.6.17 | 6.12.104 | ff3cb05289b8 |
| 2.6.17 | 6.18.45 | 3b2231e358d2 |
| 2.6.17 | 7.1.9 | da64ed1f346b |
| 2.6.17 | 7.2 | d1ad8fb2ac6a |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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
- The flaw is reached from inbound ICMPv6 Router Advertisements on the standard IPv6 receive path (ip6_input→icmpv6_rcv→ndisc_rcv→ndisc_router_discovery→rt6_route_rcv), so a network peer can trigger it on hosts accepting RAs (phones, laptops, IoT, containers on shared L2).
- AC:LAttack complexity, low
- Once the victim accepts non-zero Route Information prefixes, an attacker fully controls prefix_len and option length in forged RAs and can deterministically trigger the out-of-bounds read (up to 8 bytes) without races or uncontrollable memory layout.
- PR:NPrivileges required, none
- Exploitation requires only sending crafted ICMPv6 RAs on the victim's link; the attacker needs no account, capabilities, or init-namespace root on the target, only the ability to inject ND traffic the host will process.
- UI:NUser interaction, none
- No victim user action is required beyond normal IPv6 connectivity; RA/Route Information processing runs automatically in the kernel when accept_ra and related sysctls permit it.
- S:UScope, unchanged
- Impact is confined to kernel IPv6 routing state leaking into the same host's userspace route table; it does not cross VM, container, or IOMMU security boundaries into a separate authority.
- C:HConfidentiality impact, high
- ipv6_addr_prefix() performs an out-of-bounds read of up to eight bytes past the Route Information option (from following ND options or skb tailroom), and those kernel bytes are stored in the installed route prefix visible to userspace via netlink or ip -6 route.
- I:NIntegrity impact, none
- The bug is a bounded out-of-bounds read into a stack buffer followed by route installation; it does not corrupt kernel memory, enable arbitrary writes, or provide a demonstrated control-flow hijack primitive.
- A:NAvailability impact, none
- The vulnerable path only mis-handles prefix extraction and installs a route with leaked bytes; it does not cause kernel oops, panic, hang, or demonstrated denial of service beyond incorrect route data.