# CVE-2026-4115: PuTTY Ed25519 Signature ecc-ssh.c eddsa_verify signature verification

> Improper Ed25519 signature verification in PuTTY allows remote attackers to bypass authentication checks, though real-world impact is currently doubted.

- **Severity:** Medium 6.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Mar 2026
- **Updated:** 25 May 2026
- **Also known as:** DEBIAN-CVE-2026-4115, GHSA-p96h-94q2-fh5v, MGASA-2026-0210, UBUNTU-CVE-2026-4115

## What is CVE-2026-4115?

CVE-2026-4115 is a medium-severity vulnerability in PuTTY, published on 22 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature), CWE-345 (Insufficient Verification of Data Authenticity)

## Which versions are affected by CVE-2026-4115?

It affects 1 product.


Products: Putty Putty.

## How do I fix CVE-2026-4115?

Apply the vendor's patch.

## Is CVE-2026-4115 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-4115 exists.

## Other vulnerabilities in PuTTY

- [CVE-2004-1008](https://insights.sbomify.com/CVE-2004-1008/): Integer overflow in n/a (critical 10.0)
- [CVE-2019-17067](https://insights.sbomify.com/CVE-2019-17067/): Other in n/a (critical 9.8)
- [CVE-2021-36367](https://insights.sbomify.com/CVE-2021-36367/): Auth bypass in n/a (high 8.1)
- [CVE-2016-6167](https://insights.sbomify.com/CVE-2016-6167/): Other in n/a (high 7.8)
- [CVE-2021-33500](https://insights.sbomify.com/CVE-2021-33500/): Denial of service in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4115 and fix it if it is affected.

What it is: CVE-2026-4115 is a medium-severity vulnerability in PuTTY, published on 22 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-4115 exists.

Affected product: PuTTY. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-4115/ (Markdown: https://insights.sbomify.com/CVE-2026-4115/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4115
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4115
- OSV: https://osv.dev/vulnerability/CVE-2026-4115

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4115/
Summaries are generated and may contain mistakes; the official description above is the record.