PuTTY Ed25519 Signature ecc-ssh.c eddsa_verify signature verification

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Summary

CVECVE-2026-4115
StatePUBLISHED
AssignerVulDB
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-22 13:16:20 UTC
Updated2026-04-30 18:33:16 UTC
DescriptionA vulnerability was detected in PuTTY 0.83. Affected is the function eddsa_verify of the file crypto/ecc-ssh.c of the component Ed25519 Signature Handler. The manipulation results in improper verification of cryptographic signature. The attack may be performed from remote. The attack requires a high level of complexity. The exploitability is told to be difficult. The exploit is now public and may be used. The real existence of this vulnerability is still doubted at the moment. The patch is identified as af996b5ec27ab79bae3882071b9d6acf16044549. It is advisable to implement a patch to correct this issue. The vendor was contacted early, responded in a very professional manner and quickly released a patch for the affected product. However, at the moment there is no proof that this flaw might have any real-world impact.

Risk And Classification

Primary CVSS: v4.0 2.9 LOW from [email protected]

CVSS: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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS: 0.000170000 probability, percentile 0.043760000 (date 2026-05-05)

Problem Types: CWE-345 | CWE-347 | CWE-347 Improper Verification of Cryptographic Signature | CWE-345 Insufficient Verification of Data Authenticity

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary2.9LOWCVSS: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/C...
4.0CNADECLARED6.3MEDIUMCVSS: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
3.1[email protected]Primary3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
3.1CNADECLARED3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:O/RC:C
3.0CNADECLARED3.7LOWCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:O/RC:C
2.0[email protected]Secondary2.6AV:N/AC:H/Au:N/C:N/I:P/A:N
2.0CNADECLARED2.6AV:N/AC:H/Au:N/C:N/I:P/A:N/E:POC/RL:OF/RC:C

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
High
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS: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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS v3.0 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:O/RC:C

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Putty Putty 0.83 All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Na PuTTY affected 0.83 Not specified

References

ReferenceSourceLinkTags
www.rfc-editor.org/rfc/rfc8032 [email protected] www.rfc-editor.org Technical Description
github.com/py-thok/putty-ed25519-malleability-s-plus-l/blob/main/poc.py [email protected] github.com Exploit
vuldb.com [email protected] vuldb.com Third Party Advisory, VDB Entry
git.tartarus.org [email protected] git.tartarus.org Permissions Required
www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/eddsa-overlarge-s.html [email protected] www.chiark.greenend.org.uk Third Party Advisory
github.com/py-thok/putty-ed25519-malleability-s-plus-l [email protected] github.com Third Party Advisory
vuldb.com [email protected] vuldb.com Third Party Advisory, VDB Entry
vuldb.com [email protected] vuldb.com Permissions Required, VDB Entry
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: pythok (VulDB User) (en)

CNA: VulDB (en)

Additional Advisory Data

SourceTimeEvent
CNA2026-03-22T00:00:00.000ZAdvisory disclosed
CNA2026-03-22T01:00:00.000ZVulDB entry created
CNA2026-03-22T12:54:35.000ZVulDB entry last update
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