CVE-2019-18282

The flow_dissector feature in the Linux kernel 4.3 through 5.x before 5.3.10 has a device tracking vulnerability, aka CID-55667441c84f. This occurs because the auto flowlabel of a UDP IPv6 packet relies on a 32-bit hashrnd value as a secret, and because jhash (instead of siphash) is used. The hashrnd value remains the same starting from boot time, and can be inferred by an attacker. This affects net/core/flow_dissector.c and related code.

Weakness

The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers.

Affected Software

Potential Mitigations

• Use a well-vetted algorithm that is currently considered to be strong by experts in the field, and select well-tested implementations with adequate length seeds.
• In general, if a pseudo-random number generator is not advertised as being cryptographically secure, then it is probably a statistical PRNG and should not be used in security-sensitive contexts.
• Pseudo-random number generators can produce predictable numbers if the generator is known and the seed can be guessed. A 256-bit seed is a good starting point for producing a “random enough” number.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/112.html
• https://cwe.mitre.org/data/definitions/485.html
• https://cwe.mitre.org/data/definitions/59.html

References

• https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.3.10
• https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=55667441c84fa5e0911a0aac44fb059c15ba6da2
• https://lists.debian.org/debian-lts-announce/2020/03/msg00001.html
• https://security.netapp.com/advisory/ntap-20200204-0002/
• https://www.computer.org/csdl/proceedings-article/sp/2020/349700b594/1j2LgrHDR2o