CVE-2013-4207: Buffer overflow in sshbn.c in PuTTY before 0.63 allows remote SSH servers to cause a denial of service (crash)

Q: How do I fix CVE-2013-4207?

putty: downgrade or apply the listed mitigation; putty: upgrade to newer than 0.62. Exact commands for each OS are on this page.

Q: Is CVE-2013-4207 being exploited?

CVE-2013-4207 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2013-4207 affect?

CVE-2013-4207 affects putty, putty. Severity is medium (CVSS 4.3). Buffer overflow in sshbn.c in PuTTY before 0.63 allows remote SSH servers to cause a denial of service (crash) via an invalid DSA signature that is not properly handled during computation of a modular inverse and triggers the overflow durin

Q: How urgent is CVE-2013-4207?

Priority 35/100. No elevated risk signals yet.

Routine

MEDIUM 4.3DOWNGRADEUPGRADE

CVE-2013-4207 is a medium-severity flaw (CVSS 4.3) affecting putty, putty. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Buffer overflow in sshbn.c in PuTTY before 0.63 allows remote SSH servers to cause a denial of service (crash) via an invalid DSA signature that is not properly handled during computation of a modular inverse and triggers the overflow during a division by zero by the bignum functionality, a different vulnerability than CVE-2013-4206.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
EPSS exploit chance	1.8% (top 21%)
CISA exploited list	No
Weakness	CWE-119
Published	2013-08-19
Last modified	2026-06-16

Publisher (CNA): Red Hat, Inc. · Vendor: putty · simon tatham

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2013-08-19 23:55 UTCPublished CVE record published
2026-06-16 23:56 UTCUpdated Record last modified

putty putty DOWNGRADE

Affected: 0.45 · 0.46 · 0.47 · 0.48 · 0.49 · 0.50 · 0.51 · 0.52

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.45

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 0.45 (Debian / Ubuntu)

apt-cache madison putty sudo apt install putty=<VERSION_BEFORE_0.45> sudo apt-mark hold putty

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

dnf --showduplicates list putty sudo dnf downgrade putty-<VERSION_BEFORE_0.45> 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.

simon tatham putty UPGRADE

Affected: <= 0.62 · 0.53

Fixed in: newer than 0.62

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 0.62 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade putty

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade putty

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2013-4207?

putty: downgrade or apply the listed mitigation; putty: upgrade to newer than 0.62. Exact commands for each OS are on this page.

Is CVE-2013-4207 being exploited?

CVE-2013-4207 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-2013-4207 affect?

CVE-2013-4207 affects putty, putty. Severity is medium (CVSS 4.3). Buffer overflow in sshbn.c in PuTTY before 0.63 allows remote SSH servers to cause a denial of service (crash) via an invalid DSA signature that is not properly handled during computation of a modular inverse and triggers the overflow durin

How urgent is CVE-2013-4207?

Priority 35/100. No elevated risk signals yet.

Software pages

PuTTY vulnerabilities

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References

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