CVE-2013-4206

What it is

Heap-based buffer underflow in the modmul function in sshbn.c in PuTTY before 0.63 allows remote SSH servers to cause a denial of service (crash) and possibly trigger memory corruption or code execution via a crafted DSA signature, which is not properly handled when performing certain bit-shifting operations during modular multiplication.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

2.5% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2013-08-19 23:55 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-16 23:56 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 2.5% in the next 30 days (EPSS).
• Severity: 6.8 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2013-08-19 23:55 UTC

Last modified

2026-06-16 23:56 UTC

Exploit probability

2.5% · EPSS, next 30 days

Weakness

CWE-119 · Buffer errors

Record status

Modified

Affected

• Putty 0.45
• Putty 0.46
• Putty 0.47
• Putty 0.48
• Putty 0.49
• Putty 0.50
• Putty 0.51
• Putty 0.52

Attack profile CVSS 2.0 · 6.8

Attack vector

Network

Complexity

Medium

Authentication

None

Confidentiality

Partial

Integrity

Partial

Availability

Partial

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2013-4206.md and follow it. Check whether this project is affected by CVE-2013-4206. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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