Access-control bypass via invalid CIDR fail-open
Published Sep 23, 2026 · Updated Sep 23, 2026
Access-control bypass in BusyBox httpd in Red Hat Hardened Images allows remote attackers to reach content denied by invalid CIDR rules. The deny-rule parser accepts an out-of-range prefix length, leaves the parsed address with a zeroed mask, and installs a rule that matches no client. Exposure requires httpd to use an affected deny rule; valid rules and deployments without IP-based denial are not implicated.
Summary
What happened
Access-control bypass in BusyBox httpd in Red Hat Hardened Images allows remote attackers to reach content denied by invalid CIDR rules. The deny-rule parser accepts an out-of-range prefix length, leaves the parsed address with a zeroed mask, and installs a rule that matches no client. Exposure requires httpd to use an affected deny rule; valid rules and deployments without IP-based denial are not implicated.
The record
- CVE
- CVE-2026-88831
- Published
- Sep 23, 2026
- Updated
- Sep 23, 2026
- Vendor
- Commonhaus Foundation
- Product
- Red Hat Hardened Images
- Classifications
- T1190
- Attack vector
- network
- Privileges
- Unavailable
Timeline
How it unfolded
- Sep 23, 2026CVE publishedPublication date reported by the CVE source.
- Sep 23, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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