Is CVE-2016-6263 in the CISA KEV catalog?

No. CVE-2016-6263 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2016-6263?

CVE-2016-6263 has a CVSS v3 base score of 7.5 (HIGH).

What is the EPSS score for CVE-2016-6263?

CVE-2016-6263 has an EPSS score of 3.91% (89th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2016-6263?

Upgrade libidn on debian 11 to 1.33-1 or later. Fixes are available for 3 affected products.

CVE & CISA-KEV Catalog

CVE-2016-6263

HIGHEPSS 89th pctl

7.5

CVSS v3

NVD

Description

The stringprep_utf8_nfkc_normalize function in lib/nfkc.c in libidn before 1.33 allows context-dependent attackers to cause a denial of service (out-of-bounds read and crash) via crafted UTF-8 data.

CWE-125Out-of-bounds Read

How to fix

Remediation Available

libidnDebian

Fixed in:1.33-1CVE-2016-6263

libidnUbuntu

Fixed in:1.28-1ubuntu2.1USN-3068-1

Fixed in:1.32-3ubuntu1.1USN-3068-1

libidn11Ubuntu

Fixed in:1.28-1ubuntu2.1USN-3068-1

Fixed in:1.32-3ubuntu1.1USN-3068-1

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploit Intelligence

3.91%probability of exploitation in 30 days

89thpercentile

Elevated risk: more likely to be exploited than 89% of all known CVEs.

References

Patch1

git.savannah.gnu.org

Vendor Advisory1

lists.gnu.org

Third-Party Advisory6

Other references4

Related Vulnerabilities

Other CWE-125 (Out-of-bounds Read) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2014-0160	High	7.5	100%	KEV	Fix
CVE-2025-5777	High	7.5	100%	KEV + Ransom	Fix
CVE-2021-4034	High	7.8	95%	KEV	Fix
CVE-2023-21769	High	7.5	92%	-	Fix
CVE-2023-49285	High	8.6	89%	-	Fix
CVE-2020-8794	Critical	9.8	89%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-06.