CVE-2026-4115: A vulnerability was detected in PuTTY 0.83

This week

LOW 3.7REMOTEDOWNGRADE

CVE-2026-4115 is a low-severity flaw (CVSS 3.7) affecting putty. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	3.7 (Low)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 54%)
CISA exploited list	No
Weakness	CWE-345, CWE-347
Published	2026-03-22
Last modified	2026-06-17

Publisher (CNA): VulDB · Vendor: putty

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-22 13:16 UTCPublished CVE record published
2026-06-17 10:56 UTCUpdated Record last modified

putty putty DOWNGRADE

Affected: 0.83

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.83

1. Check installed version

apt-cache policy putty || rpm -q putty || putty --version

2. No fixed release: DOWNGRADE to a release before 0.83 (Debian / Ubuntu)

apt-cache madison putty sudo apt install putty=<VERSION_BEFORE_0.83> sudo apt-mark hold putty

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list putty sudo dnf downgrade putty-<VERSION_BEFORE_0.83> sudo dnf versionlock add putty

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-4115?

putty: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-4115 being exploited?

CVE-2026-4115 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-4115 affect?

CVE-2026-4115 affects putty. Severity is low (CVSS 3.7). 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 att

How urgent is CVE-2026-4115?

Priority 34/100. Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PuTTY vulnerabilities

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References

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