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CVE-2024-31497 is a cryptographic vulnerability in PuTTY 0.68 through 0.80, fixed in 0.81, affecting ECDSA signatures made with NIST P-521 keys. The flaw is caused by biased nonce generation during ECDSA signing: the generated nonces are not uniformly random, and the first 9 bits of each nonce are zero. This leakage is sufficient for practical lattice-based attacks that recover the underlying private key after observing roughly 60 valid signatures produced by the same P-521 key. The issue affects PuTTY and related components such as Pageant, and also impacts third-party software that bundled the vulnerable PuTTY code, including affected versions of FileZilla, WinSCP, TortoiseGit, and TortoiseSVN. The vulnerability is especially dangerous where an attacker can collect signatures over time, such as from SSH authentication to a malicious server or from publicly visible signed Git operations performed through agent forwarding.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos (1 hidden).
This repository is a proof-of-concept (POC) exploit for CVE-2024-31497, a vulnerability in the ECDSA nonce generation of PuTTY and TortoiseGit (ecc-ssh.c). The exploit leverages the bias in the nonce (top 9 bits zeroed) to recover the ECDSA private key using lattice-based cryptanalysis (Hidden Number Problem). The repository is structured as follows: - 'main.py' is the main entry point, taking as input a file of ECDSA signatures and a public key, and attempts to recover the private key, saving it to disk if successful. - 'attack/ecdsa_hnp.py' contains the core cryptanalytic logic for solving the Hidden Number Problem with biased ECDSA nonces. - 'attack/exploit.py' provides functions for key export and public key reading. - 'attack/usvp.py' and 'attack/utils.py' provide supporting cryptanalytic and utility functions. - 'test.py' is a test harness that generates test signatures and validates the attack. - 'test/signatures.txt' and 'test/pubkey.pub' are sample input files. The exploit requires at least 58-60 ECDSA signatures generated by a vulnerable implementation and the corresponding public key. It does not target a network service directly, but the README describes two attack surfaces: collecting signatures from signed GitHub commits or by running a rogue SSH server to collect signatures from clients using the vulnerable software. The exploit is a POC and does not include weaponized automation for signature collection, but demonstrates full private key recovery from collected data.
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An ECDSA nonce vulnerability referenced as a similar class example in the article's resource section.
A vulnerability in PuTTY (CVE-2024-31497) allows attackers to recover SSH keys, aiding persistence and lateral movement in compromised environments.
A cryptographic flaw in PuTTY/Pageant where biased ECDSA nonce generation for NIST P-521 can allow private key recovery from a relatively small number of observed signatures, enabling subsequent unauthorized access and potential supply-chain compromise (e.g., via signed Git commits).
A cryptographic vulnerability in PuTTY’s ECDSA (NIST P-521) nonce generation where nonces are biased (first 9 bits zero), enabling lattice-based recovery of the ECDSA private key after observing ~60 signatures produced under the same key.
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Cross-references every affected SKU, including bundled OEM variants.
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