CVE-2015-5309: Integer overflow in the terminal emulator in PuTTY before 0.66 allows remote attackers to cause a denial of se

Q: How do I fix CVE-2015-5309?

leap: mitigate or apply the listed mitigation; opensuse: mitigate or apply the listed mitigation; putty: upgrade to newer than 0.65. Exact commands for each OS are on this page.

Q: Is CVE-2015-5309 being exploited?

CVE-2015-5309 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-2015-5309 affect?

CVE-2015-5309 affects leap, opensuse, putty. Severity is medium (CVSS 4.3). Integer overflow in the terminal emulator in PuTTY before 0.66 allows remote attackers to cause a denial of service (memory corruption) or possibly execute arbitrary code via an ECH (erase characters) escape sequence with a large parameter

Q: How urgent is CVE-2015-5309?

Priority 37/100. No elevated risk signals yet.

Routine

MEDIUM 4.3MITIGATEMITIGATEUPGRADE

CVE-2015-5309 is a medium-severity flaw (CVSS 4.3) affecting leap, opensuse, putty. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Integer overflow in the terminal emulator in PuTTY before 0.66 allows remote attackers to cause a denial of service (memory corruption) or possibly execute arbitrary code via an ECH (erase characters) escape sequence with a large parameter value, which triggers a buffer underflow.

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	3.5% (top 11%)
CISA exploited list	No
Weakness	CWE-189
Published	2015-12-07
Last modified	2026-06-17

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

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

Am I affected?

Timeline

2015-12-07 20:59 UTCPublished CVE record published
2026-06-17 00:28 UTCUpdated Record last modified

opensuse leap MITIGATE

Affected: 42.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 42.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

opensuse opensuse MITIGATE

Affected: 13.1 · 13.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 13.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

simon tatham putty UPGRADE

Affected: <= 0.65

Fixed in: newer than 0.65

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 0.65 (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-2015-5309?

leap: mitigate or apply the listed mitigation; opensuse: mitigate or apply the listed mitigation; putty: upgrade to newer than 0.65. Exact commands for each OS are on this page.

Is CVE-2015-5309 being exploited?

CVE-2015-5309 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-2015-5309 affect?

CVE-2015-5309 affects leap, opensuse, putty. Severity is medium (CVSS 4.3). Integer overflow in the terminal emulator in PuTTY before 0.66 allows remote attackers to cause a denial of service (memory corruption) or possibly execute arbitrary code via an ECH (erase characters) escape sequence with a large parameter

How urgent is CVE-2015-5309?

Priority 37/100. No elevated risk signals yet.

Software pages

PuTTY vulnerabilities

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References

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