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Vulnerability record · CVE-2026-4115 · published 22 March 2026

CVE-2026-4115: Putty insufficient verification of data authenticity vulnerability

Putty · Putty

A 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.

2.9 CVSS 4.0 Low EPSS 0.24% · top 86.3% CWE-345 · Insufficient verification of data authenticityCWE-347 · Improper verification of cryptographic signature
2.9CVSS 4.0 base score, v2 2.6
0.24%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
9References, 1 tagged exploit
17 Jun 2026Last modified by NVD

Description

A 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.

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:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://git.tartarus.org/?p=simon/putty.git;a=commitdiff;h=af996b5ec27ab79bae3882071b9d6acf16044549 Permissions Required
https://github.com/py-thok/putty-ed25519-malleability-s-plus-l Third Party Advisory
https://github.com/py-thok/putty-ed25519-malleability-s-plus-l/blob/main/poc.py Exploit
https://vuldb.com/?ctiid.352429 Permissions RequiredVDB Entry
https://vuldb.com/?id.352429 Third Party AdvisoryVDB Entry
https://vuldb.com/?submit.775576 Third Party AdvisoryVDB Entry
https://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/eddsa-overlarge-s.html Third Party Advisory
https://www.rfc-editor.org/rfc/rfc8032#section-8.4 Technical Description
http://www.openwall.com/lists/oss-security/2026/05/24/11

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2004-1008Putty vulnerabilityInteger signedness error in the ssh2_rdpkt function in PuTTY before 0.56 allows remote attackers to execute arbitrary code via a SSH2_MSG_DEBUG packe…EPSS 7.4%10.0CVE-2002-1357Cisco ios memory buffer overflow vulnerabilityMultiple SSH2 servers and clients do not properly handle packets or data elements with incorrect length specifiers, which may allow remote attackers …EPSS 9.8%10.0CVE-2002-1358Cisco ios improper input validation vulnerabilityMultiple SSH2 servers and clients do not properly handle lists with empty elements or strings, which may allow remote attackers to cause a denial of …EPSS 5.8%10.0CVE-2002-1359SSH2 implementations mishandle large packets, enabling DoS and possible code executionMultiple SSH2 servers and clients fail to properly handle large packets or large fields, leading to buffer overflow conditions. The flaw was demonstr…EPSS 80%analysed10.0CVE-2002-1360Cisco ios improper input validation vulnerabilityMultiple SSH2 servers and clients do not properly handle strings with null characters in them when the string length is specified by a length field, …EPSS 6.1%9.8CVE-2019-17067Putty allocation without limits vulnerabilityPuTTY before 0.73 on Windows improperly opens port-forwarding listening sockets, which allows attackers to listen on the same port to steal an incomi…EPSS 1.6%9.8CVE-2019-9895Putty memory buffer overflow vulnerabilityIn PuTTY versions before 0.71 on Unix, a remotely triggerable buffer overflow exists in any kind of server-to-client forwarding.EPSS 2.6%9.8CVE-2019-9898Putty vulnerabilityPotential recycling of random numbers used in cryptography exists within PuTTY before 0.71.EPSS 3.9%

Source: NIST National Vulnerability Database (record CVE-2026-4115), CISA KEV, FIRST EPSS (scores of 2026-09-29). This page is refreshed as NVD updates the record.