CVE-2024-31497 PoC — PuTTY 安全漏洞

Title:PuTTY 安全漏洞 (CVE-2024-31497)
Description:In PuTTY 0.68 through 0.80 before 0.81, biased ECDSA nonce generation allows an attacker to recover a user's NIST P-521 secret key via a quick attack in approximately 60 signatures. This is especially important in a scenario where an adversary is able to read messages signed by PuTTY or Pageant. The required set of signed messages may be publicly readable because they are stored in a public Git service that supports use of SSH for commit signing, and the signatures were made by Pageant through an agent-forwarding mechanism. In other words, an adversary may already have enough signature information to compromise a victim's private key, even if there is no further use of vulnerable PuTTY versions. After a key compromise, an adversary may be able to conduct supply-chain attacks on software maintained in Git. A second, independent scenario is that the adversary is an operator of an SSH server to which the victim authenticates (for remote login or file copy), even though this server is not fully trusted by the victim, and the victim uses the same private key for SSH connections to other services operated by other entities. Here, the rogue server operator (who would otherwise have no way to determine the victim's private key) can derive the victim's private key, and then use it for unauthorized access to those other services. If the other services include Git services, then again it may be possible to conduct supply-chain attacks on software maintained in Git. This also affects, for example, FileZilla before 3.67.0, WinSCP before 6.3.3, TortoiseGit before 2.15.0.1, and TortoiseSVN through 1.14.6.

Proof Of Concept that exploits PuTTy CVE-2024-31497.

# CVE-2024-31497 POC

This vulnerability exploits the biased ECDSA nonce generation in the ```ecc-ssh.c``` file. The nonce is generated with $sha512(ID\ ||\ sha512(privKey)\ ||\ sha1(data))\ mod\ q$ leaving the top 9 bits to zero. In order to recover the private key we need 60 signatures but with 58 we still have 50% probability of success.

 Vuln discovered by Bäumer and Marcus Brinkmann.  


## Requirements

In order to use this exploit you must have [sagemath](https://github.com/sagemath/sage/) and the python dependencies in ```requirements.txt``` installed. 


## Attack Surface

1. Extract the ECDSA signatures from 60 verified GitHub commits that used PuTTy or TortoiseGit to sign the commit content. 

2. Another possible attack is to set up a rogue SSH server where victims connect (using PuTTY or Pageant) and after several connections you can retrieve the 60 signatures to recover the private key. 

## Arguments

- The signature file must contain the **message hash**, a space and the values of **r** and **s** concatenated.

- The **pubkey** file input, can be in raw, PEM, DER or OpenSSH format.

## Acknowledgements

This poc uses part of the [malb](https://github.com/malb) implementation of the paper [On Bounded Distance Decoding with Predicate: Breaking the "Lattice Barrier" for the Hidden Number Problem](https://eprint.iacr.org/2020/1540.pdf)

 [4.0K]  /data/pocs/e633b58ef641e0bd9a76e8f56cdd4716f9d69b8f
├── [4.0K]  attack
│   ├── [ 22K]  ecdsa_hnp.py
│   ├── [1.1K]  exploit.py
│   ├── [ 31K]  usvp.py
│   └── [1003]  utils.py
├── [2.5K]  main.py
├── [1.3K]  README.md
├── [  74]  requirements.txt
├── [4.0K]  test
│   ├── [ 267]  pubkey.pub
│   └── [ 23K]  signatures.txt
└── [ 557]  test.py

2 directories, 10 files