Is CVE-2026-4115 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-4115 being exploited in the wild.

How severe is CVE-2026-4115?

Low severity, with a CVSS score of 3.7, published 22 March 2026.

Is there a fix for CVE-2026-4115?

A patch was published on 2026-03-22: Vendor released fix in version 0.84 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-4115 attacked?

It is attacked over the network, in a network appliance.

Am I affected by CVE-2026-4115?

Check whether you run Putty at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-4115: PuTTY Ed25519 signature malleability in eddsa_verify

CVE-2026-4115 · Severity: low · CVSS 3.7 · Published 2026-03-22

PuTTY is a widely used open-source terminal emulator and network file transfer application. A flaw was identified in how it verifies digital signatures for certain secure connections (Ed25519). While an attacker could technically modify a valid signature into a different but still 'valid' format, there is currently no evidence that this allows for unauthorized access or data theft in real-world SSH scenarios.

Technologies: Putty. Vendors: Putty.

Quick answers

Is CVE-2026-4115 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-4115 being exploited in the wild.
How severe is CVE-2026-4115?: Low severity, with a CVSS score of 3.7, published 22 March 2026.
Which products and versions are affected?: Putty 0.68 through 0.83.
Is there a fix for CVE-2026-4115?: A patch was published on 2026-03-22: Vendor released fix in version 0.84 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-4115 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-4115?: Check whether you run Putty at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A signature malleability vulnerability exists in PuTTY's Ed25519 signature handler within `crypto/ecc-ssh.c`. The `eddsa_verify` function fails to strictly enforce the RFC 8032 requirement that the 's' value be less than the curve's base point order (L). Instead, PuTTY reduces overlarge values of 's' modulo L, allowing an attacker to modify a valid signature into a non-canonical but accepted form. While this violates 'strong unforgeability' (SUF-CMA), the vendor disputes the practical impact in the context of SSH, as the signature bits are not used as input for subsequent session keys or MACs. A patch was released in version 0.84 (commit af996b5).

Affected products

PuTTY PuTTY 0.68 through 0.83

Timeline

2026-02: disclosed: Reported to vendor via email
2026-03-22: advisory: Public disclosure and CVE assignment
2026-03-22: patched: Vendor released fix in version 0.84

References

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