GHSA-52xf-5p2m-9wrv s2n-tls has a potentially observable differences in RSA premaster secret handling

Q: Which versions are affected by GHSA-52xf-5p2m-9wrv?

2 open source packages ship an affected version, including s2n-tls.

Q: Is GHSA-52xf-5p2m-9wrv being exploited?

There is no known exploitation of GHSA-52xf-5p2m-9wrv in the wild and no public exploit code.

Q: How do I fix GHSA-52xf-5p2m-9wrv?

Upgrade s2n-tls to 0.2.7 or later.

Not scored Published 6 Jun 2024

Timing side-channel in s2n-tls RSA key exchange allows theoretical decryption of premaster secrets, affecting servers using RSA ciphers without blinding.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is GHSA-52xf-5p2m-9wrv?

GHSA-52xf-5p2m-9wrv is a vulnerability in s2n-tls, published on 6 Jun 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

When receiving a message from a client that sent an invalid RSA premaster secret, an issue in s2n-tls results in the server performing additional processing when the premaster secret contains an incorrect client hello version. While no practical attack on s2n-tls has been demonstrated, this causes a small timing difference which could theoretically be used as described in the Marvin Attack [1].

We would like to thank Hubert Kario [2] for reporting this issue.

Impact

The extent of this issue is a timing difference. No practical attack on s2n-tls has been demonstrated.

This issue affects server applications that permit RSA key exchange. Applications that use the default, built-in blinding feature or properly implement self-service blinding are not affected.

Impacted versions: <= v1.4.15.

Patches

The patch is included in v1.4.16 [3].

Workarounds

Applications can work around this issue by using an s2n-tls security policy that disallows RSA key exchange.

If you have any questions or comments about this advisory we ask that you contact AWS/Amazon Security via our vulnerability reporting page [4] or directly via email to [email protected]. Please do not create a public GitHub issue.

[1] https://people.redhat.com/~hkario/marvin/ [2] https://github.com/tomato42 [3] https://github.com/aws/s2n-tls/releases/tag/v1.4.16 [4] https://aws.amazon.com/security/vulnerability-reporting

Which versions are affected by GHSA-52xf-5p2m-9wrv?