CVE-2016-2563: Stack-based buffer overflow in the SCP command-line utility in PuTTY before 0.67 and KiTTY 0.66.6.3 and earlie

Q: How do I fix CVE-2016-2563?

kitty: upgrade to newer than 0.66.6.3; putty: upgrade to newer than 0.66. Exact commands for each OS are on this page.

Q: Is CVE-2016-2563 being exploited?

CVE-2016-2563 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-2016-2563 affect?

CVE-2016-2563 affects kitty, putty. Severity is critical (CVSS 9.8). Stack-based buffer overflow in the SCP command-line utility in PuTTY before 0.67 and KiTTY 0.66.6.3 and earlier allows remote servers to cause a denial of service (stack memory corruption) or execute arbitrary code via a crafted SCP-SINK fi

Q: How urgent is CVE-2016-2563?

Priority 69/100. Critical severity; EPSS top 2%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADEUPGRADE

CVE-2016-2563 is a critical-severity flaw (CVSS 9.8) affecting kitty, putty. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Stack-based buffer overflow in the SCP command-line utility in PuTTY before 0.67 and KiTTY 0.66.6.3 and earlier allows remote servers to cause a denial of service (stack memory corruption) or execute arbitrary code via a crafted SCP-SINK file-size response to an SCP download request.

Why this priority

Critical severity
EPSS top 2%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	32.8% (top 2%)
CISA exploited list	No
Weakness	CWE-119
Published	2016-04-07
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: 9bis · simon tatham

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

Am I affected?

Timeline

2016-04-07 23:59 UTCPublished CVE record published
2026-06-17 00:44 UTCUpdated Record last modified

9bis kitty UPGRADE

Affected: <= 0.66.6.3

Fixed in: newer than 0.66.6.3

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 0.66.6.3 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade kitty

Note

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

simon tatham putty UPGRADE

Affected: <= 0.66

Fixed in: newer than 0.66

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 0.66 (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.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: Putty pscp 0.66 - Stack Buffer Overwrite

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-2016-2563?

kitty: upgrade to newer than 0.66.6.3; putty: upgrade to newer than 0.66. Exact commands for each OS are on this page.

Is CVE-2016-2563 being exploited?

CVE-2016-2563 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-2016-2563 affect?

CVE-2016-2563 affects kitty, putty. Severity is critical (CVSS 9.8). Stack-based buffer overflow in the SCP command-line utility in PuTTY before 0.67 and KiTTY 0.66.6.3 and earlier allows remote servers to cause a denial of service (stack memory corruption) or execute arbitrary code via a crafted SCP-SINK fi

How urgent is CVE-2016-2563?

Priority 69/100. Critical severity; EPSS top 2%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PuTTY vulnerabilities

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References

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