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GHSA-79rc-jjh6-rc89
No affected components available
Impact
The server uses ECDH to calculate a shared secret for the symmetric encryption key used to encrypt network packets after logging in. ECDH requires that the keys used must both belong to the same elliptic curve. In Minecraft: Bedrock Edition, the curve used is secp384r1.
Using any other curve (for example secp256r1) to sign the LoginPacket JWTs would lead to successfully verifying the login chain, but would later crash due to an uncaught exception during ECDH key derivation due to the client-provided key belonging to a different curve than the server's key. It's also theoretically possible that a non-EC key could be used (e.g. RSA or DH), which would also pass login verification as long as SHA384 hashing algorithm was used for the JWT signatures, and also lead to a crash.
Patches
The problem was fixed in 4.23.1 and 5.3.1 in the following commit: 4e646d19a4a1e0d082bd4d1f5a58ae0182a268d9 While 4.x would not have crashed when this was encountered, the faulty validation code has also been corrected there.
Workarounds
A plugin could handle LoginPacket and check that all of the identityPublicKeys provided in the JWT bodies actually belong to secp384r1. This can be checked by verifying that openssl_pkey_get_details($key)["ec"]["curve_name"] is set and equal to secp384r1. Beware that this element may not exist if the key is not an EC key at all.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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