Security readout for executives and security teams
Plain-English summary
This flaw affects uClibc and uClibc-ng DNS name handling before 1.0.39. A malicious or compromised DNS response could make software trust or display the wrong hostname, or pass unsafe text into an application. Business risk is highest for embedded and networked products built on these libraries.
Executive priority
Treat this as high-priority for embedded product and appliance fleets, especially where firmware refresh cycles are slow. The issue is critical, but urgency should be based on confirmed uClibc/uClibc-ng usage and vendor fix availability.
Technical view
The stub resolver fails to validate special characters in domain names returned through gethostbyname, getaddrinfo, gethostbyaddr, and getnameinfo. The CVE describes possible hostname confusion and application injection impacts, including remote code execution, XSS, and crashes, depending on how resolver output is consumed.
Likely exposure
Exposure is most likely in embedded Linux firmware, appliances, routers, IoT devices, or custom systems that include uClibc or uClibc-ng before 1.0.39 and call the affected resolver APIs.
Exploitation context
The supplied bundle does not show CISA KEV listing or active exploitation. Exploitation would depend on an attacker influencing DNS responses and on an application using returned hostnames unsafely.
Researcher notes
The affected products field in the bundle is incomplete, but the description names uClibc and uClibc-ng before 1.0.39. The listed CWE-79 captures injection/XSS impact, while the resolver validation failure is broader and can affect hostname integrity.
Mitigation direction
- Inventory products and firmware using uClibc or uClibc-ng resolver code.
- Update uClibc-ng to 1.0.39 or a vendor-fixed build where available.
- For legacy uClibc, check vendor or maintainer guidance for backported fixes.
- Prioritize internet-facing, DNS-dependent, and remotely administered embedded products.
- Reduce reliance on untrusted DNS responses where operationally feasible.
Validation and detection
- Confirm libc implementation and version from SBOMs, firmware manifests, or vendor documentation.
- Identify applications calling affected resolver APIs in exposed product paths.
- Verify the referenced uClibc-ng fix or equivalent backport is present.
- Check vendor advisories for affected device models and firmware releases.
- Review logs and telemetry for unusual DNS-related crashes or hostname anomalies.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-43523 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H2.86Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.6CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://uclibc-ng.org/CVE reference · x_refsource_MISC
- https://github.com/wbx-github/uclibc-ng/commit/0f822af0445e5348ce7b7bd8ce1204244f31d174CVE reference · x_refsource_MISC
- https://www.openwall.com/lists/oss-security/2021/11/09/1CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.