CVE-2026-74598

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

ipv6: fix Route Information option length validation

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)

# foll

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References