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CVE-2021-43523

30
FAUCET Score

CVE-2021-43523 is a critical vulnerability in uClibc and uClibc-ng versions prior to 1.0.39, stemming from improper handling of special characters in DNS responses. This flaw can lead to domain hijacking, remote code execution, XSS, or application crashes due to incorrect hostname output or injection into applications. With a CVSS score of 9.6 (Critical), it presents a significant risk, requiring user interaction and impacting confidentiality, integrity, and availability. While no active exploitation, public exploit code, or significant community discussion has been observed, the potential impact remains severe.

Impacted Technologies

VendorProductVersion(s)CPE
<= 0.9.33.2CPE matchmatch criteria
cpe:2.3:a:uclibc:uclibc:*:*:*:*:*:*:*:*
< 1.0.39CPE matchmatch criteria
cpe:2.3:a:uclibc-ng_project:uclibc-ng:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.6CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.8
Impact Score
6.0
CvssVersion
3.1

Exploit Intelligence

EPSS Score
3.26%
Probability of exploitation in next 30 days
EPSS Percentile
87.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0326 is in the 92nd percentile among its peer group of 834 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.8 Bluesky, 0.5 Mastodon, and 1.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.1 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (5)

github_advisorypatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: 18963-16820Fixed in: 1.0.37-2
microsoftpatch availablevia msrc
Product: 18964-16823Fixed in: 1.0.37-2
microsoftpatch availablevia msrc
Product: cm1 uclibc-ng 1.0.37-2 on CBL Mariner 1.0Fixed in: 1.0.37-2
microsoftpatch availablevia msrc
Product: cbl2 uclibc-ng 1.0.37-2 on CBL Mariner 2.0Fixed in: 1.0.37-2

Vendor Advisories (1)

microsoft2021-Nov/CVE-2021-43523Critical

In uClibc and uClibc-ng before 1.0.39 incorrect handling of special characters in domain names returned by DNS servers via gethostbyname getaddrinfo gethostbyaddr and getnameinfo can lead to output of wrong hostnames (leading to domain hijacking) or injection into applications (leading to remote code execution XSS applications crashes etc.). In other words a validation step which is expected in any stub resolver does not occur.

Nov 9, 2021

References

github.com / wbx-github/uclibc-ng/commit/0f822af0445e5348ce7b7bd8ce1204244f31d174
PatchThird Party Advisory
uclibc-ng.org
Vendor Advisory
openwall.com / lists/oss-security/2021/11/09/1
ExploitMailing ListThird Party Advisory