Busybox: busybox: httpd silently fails open when ip deny rules contain invalid cidr prefix lengths
Summary
| CVE | CVE-2026-88831 |
|---|---|
| State | PUBLISHED |
| Assigner | redhat |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-23 18:17:10 UTC |
| Updated | 2026-09-25 23:16:54 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.1 5.3 MEDIUM from [email protected]
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
EPSS: 0.002360000 probability, percentile 0.131640000 (date 2026-09-27)
Problem Types: CWE-636 | CWE-636 Not Failing Securely ('Failing Open')
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 5.3 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N |
| 3.1 | CNA | CVSS | 5.3 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
LowIntegrity
NoneAvailability
NoneCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Red Hat | Red Hat Hardened Images | unaffected 1.37.0-9.1.hum1 * rpm | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| access.redhat.com/errata/RHSA-2026:72111 | [email protected] | access.redhat.com | |
| access.redhat.com/security/cve/CVE-2026-88831 | [email protected] | access.redhat.com | |
| bugzilla.redhat.com/show_bug.cgi | [email protected] | bugzilla.redhat.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Red Hat would like to thank Shubham Raj (Causal Security) for reporting this issue. (en)
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| CNA | 2026-09-09T00:00:00.000Z | Reported to Red Hat. |
| CNA | 2026-09-23T16:35:00.000Z | Made public. |
Workarounds
CNA: 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.
There are currently no legacy QID mappings associated with this CVE.