AndresFreundTec
It seems analysis is getting somewhere: https://bsky.app/profile/did:plc:x2nsupeeo52oznrmplwapppl/post/3kowjkx2njy2b
Filippo Valsorda (@filippo.abyssdomain.expert)

I'm watching some folks reverse engineer the xz backdoor, sharing some *preliminary* analysis with permission. The hooked RSA_public_decrypt verifies a signature on the server's host key by a fixed Ed448 key, and then passes a payload to system(). It's RCE, not auth bypass, and gated/unreplayable. [contains quote post or other embedded content]

Bluesky Social
Mar 30, 2024 at 7:53pmWeb
Show threadEvan LightMar 30, 2024

@AndresFreundTec The next question to ask: how many similar attacks have been heretofore successful/gone undetected?

We enter the "proving a negative" space with that one. 😖

Show threadguentherMar 30, 2024
@AndresFreundTec I'm not sure if I understand the post correctly. It's an RCE backdoor for sshd, and the payload is inside the pubkey of a connecting client, but also it must be signed by the original backdoor author in order to be executed?
Show threadAndresFreundTecMar 30, 2024
@guenther That's how I understand it, yes
Show threadgrinMar 31, 2024
@guenther
Funky to say that but that's very considerate, preventing it to be used by the black hat masses....
Precision weapon.
@AndresFreundTec
Show threadDominic WhiteMar 31, 2024
@AndresFreundTec he posted it on mastodon too https://abyssdomain.expert/@filippo/112185827553387306
Filippo Valsorda :go: (@[email protected])

I'm watching some folks reverse engineer the xz backdoor, sharing some *preliminary* analysis with permission. The hooked RSA_public_decrypt verifies a signature on the server's host key by a fixed Ed448 key, and then passes a payload to system(). It's RCE, not auth bypass, and gated/unreplayable. More details in this thread: https://bsky.app/profile/did:plc:x2nsupeeo52oznrmplwapppl/post/3kowjkx2njy2b

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