CVE-2026-88831
Description
BusyBox httpd IP deny rules with invalid CIDR prefix lengths fail open, leaving a parsed IP with a zeroed mask so the rule matches no clients.
Statement
This flaw causes BusyBox httpd to silently ignore malformed IP deny rules, allowing network clients that should be blocked to access protected content. BusyBox httpd is rarely deployed as a production web server on Fedora, and exploitation requires a misconfigured CIDR mask in the httpd configuration file.
Mitigation
Audit all BusyBox httpd configuration files for syntactically valid CIDR prefix lengths. Implement network-level access controls (iptables/nftables) as the primary enforcement layer rather than relying on application-level ACLs.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.3 | N/A | 5.3 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | Low | N/A | Low |
| Integrity Impact | None | N/A | None |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
Intended access restrictions can be bypassed, which is often contradictory to what the product's administrator expects.
Acknowledgements
Red Hat would like to thank Shubham Raj (Causal Security) for reporting this issue.
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