CVE-2026-4115Public exploitNetwork attack vector

Signature malleability via reduced overlarge scalar

Published Mar 22, 2026 · Updated Mar 22, 2026

Improper EdDSA verification in PuTTY 0.68 through 0.83 allows remote attackers to alter valid signatures while they are in transit. The eddsa_verify function accepts an out-of-range s value by reducing it modulo the curve order instead of rejecting it. Exploitation requires on-path access and an existing valid signature; upstream reports no demonstrated SSH security consequence.

CVSS severityUnavailable
Unscored
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper EdDSA verification in PuTTY 0.68 through 0.83 allows remote attackers to alter valid signatures while they are in transit. The eddsa_verify function accepts an out-of-range s value by reducing it modulo the curve order instead of rejecting it. Exploitation requires on-path access and an existing valid signature; upstream reports no demonstrated SSH security consequence.

The record

CVE
CVE-2026-4115
Published
Mar 22, 2026
Updated
Mar 22, 2026
Vendor
PuTTY
Product
PuTTY
Classifications
CWE-347, CWE-345, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=0.83

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

PuTTY · PuTTYversion=0.83

Published CVSS scores

3.7VulDBCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:O/RC:C
2.6VulDBAV:N/AC:H/Au:N/C:N/I:P/A:N/E:POC/RL:OF/RC:C
6.3VulDBCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P
3.7VulDBCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:O/RC:C

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 exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
CWE-345Insufficient Verification of Data Authenticity
T1557Adversary-in-the-Middle

Public exploit references

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

Technologies

Your stack

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Your stack

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