CVE-2026-4115: PuTTY Ed25519 Signature ecc-ssh.c eddsa_verify signature verification
Vulnerability summary
CVE-2026-4115 is a medium (CVSS 6.3) vulnerability in putty. EPSS estimates a 0.55% chance of exploitation in the next 30 days, higher than 46.3% of scored vulnerabilities. 1 public exploit is recorded.
Not severe (CVSS 6.3, network access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Timeline
- 22-03-2026PublishedVulnerability first disclosed.
- 25-05-2026Last modifiedVulnerability information updated.
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 metrics
10 scores · 4 sources · 4 versions- OSV · UbuntuEcosystem advisory · calculated6.3MediumCVSS: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
- OSV · DebianEcosystem advisory · calculated6.3MediumCVSS: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/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
- NVDNIST2.9LowCVSS: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/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:XDiffers
- OSV · UbuntuEcosystem advisory · calculated3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- NVDNIST3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- NVDNIST2.6LowAV:N/AC:H/Au:N/C:N/I:P/A:N
EPSS trend
Probability
0.55%
Chance of exploitation in the next 30 days
Percentile
46%
Versus all other CVEs
30-day change
Increase +0.31 pp
From 0.24% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
1 foundPutty Ed25519 Malleability S Plus L
Maturity: poc
Weaknesses
CWE · root cause- CWE-345Insufficient Verification of Data AuthenticityThe product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
- CWE-347Improper Verification of Cryptographic SignatureThe product does not verify, or incorrectly verifies, the cryptographic signature for data.
Affected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Debian1 product
- puttyAll versions (No fix recorded) | < 0.84-1
Mageia1 product
- putty< 0.84-1.mga9
Putty1 product
- putty0.83
Ubuntu1 product
- puttyAll versions (No fix recorded)
4 vendors · 4 products
References
18 links- www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/eddsa-overlarge-s.htmlRelatedWEBREPORTThird Party Advisory
- git.tartarus.org?p=simon/putty.git;a=commitdiff;h=af996b5ec27ab79bae3882071b9d6acf16044549PatchREPORTPermissions Required
