CVE-2024-31497Known exploitationPublic exploitNetwork attack vector

Private-key recovery via biased P-521 nonces

Published Apr 15, 2024 · Updated Nov 4, 2025

Weak nonce generation in PuTTY 0.68 through 0.80 allows attackers to recover NIST P-521 private keys from about 60 signatures. The P-521 signing path derives each nonce in a way that forces its top nine bits to zero, enabling lattice-based key recovery. Attackers must collect signatures from public signed commits or a rogue SSH server, after which the recovered key permits impersonation wherever it is accepted.

CVSS severity5.9
Medium
EPSS probability5.77%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Weak nonce generation in PuTTY 0.68 through 0.80 allows attackers to recover NIST P-521 private keys from about 60 signatures. The P-521 signing path derives each nonce in a way that forces its top nine bits to zero, enabling lattice-based key recovery. Attackers must collect signatures from public signed commits or a rogue SSH server, after which the recovered key permits impersonation wherever it is accepted.

The record

CVE
CVE-2024-31497
Published
Apr 15, 2024
Updated
Nov 4, 2025
Vendor
PuTTY
Product
PuTTY
Classifications
CWE-338
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 15, 2024CVE publishedPublication date reported by the CVE source.
  2. Nov 4, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.68 <0.81

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

PuTTY · PuTTYversion=0.68 <0.81

Published CVSS scores

5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
5.9CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-338Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo