chap: Use proper entropy source #67
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The challenge sent to the initiator is based on a poor source of randomness, it uses rand() without seeding it by srand(). So the glibc PRNG is always seeded with 1 and as a consequence the sequence of challenges is always the same. An attacker which is able to monitor network traffic can apply a replay attack to bypass the CHAP authentication. All the attacker has to do is waiting for the server or the service to restart and replay with a previously record CHAP session which fits into the sequence. To overcome the issue, use getrandom() to query the kernel random number generator. Also always send a challenge of length CHAP_CHALLENGE_MAX, there is no benefit in sending a variable length challenge. Signed-off-by: Richard Weinberger <richard@nod.at>
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Thanks a lot! |
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This got https://www.cve.org/CVERecord?id=CVE-2024-45751 assigned |
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The challenge sent to the initiator is based on a poor source of randomness, it uses rand() without seeding it by srand(). So the glibc PRNG is always seeded with 1 and as a consequence the sequence of challenges is always the same.
An attacker which is able to monitor network traffic can apply a replay attack to bypass the CHAP authentication. All the attacker has to do is waiting for the server or the service to restart and replay with a previously record CHAP session which fits into the sequence.
To overcome the issue, use getrandom() to query the kernel random number generator.
Also always send a challenge of length CHAP_CHALLENGE_MAX, there is no benefit in sending a variable length challenge.