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CVE-2026-8856 IBM CVE debrief

IBM HTTP Server versions 8.5 (prior to 8.5.5.30) and 9.0 (prior to 9.0.5.29) contain a denial-of-service vulnerability exploitable when an attacker has write access to portions of the server configuration. The CVSS 3.1 vector (AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H) indicates a local attack vector with low attack complexity, no privileges required, and no user interaction needed, resulting in high impact to integrity and availability but no confidentiality impact. The weakness is categorized as CWE-400 (Uncontrolled Resource Consumption). IBM has released a vendor advisory with remediation guidance. Organizations should apply the vendor-provided fixes and restrict configuration file permissions to authorized administrative accounts only.

Vendor
IBM
Product
HTTP Server
CVSS
HIGH 7.7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-26
Original CVE updated
2026-05-26
Advisory published
2026-05-26
Advisory updated
2026-05-26

Who should care

Organizations running IBM HTTP Server 8.5 or 9.0 in production environments, particularly those with shared hosting configurations or multiple administrative users who may have configuration access. System administrators responsible for web server security and availability should prioritize patching. Security teams should verify configuration file permissions as an immediate compensating control.

Technical summary

IBM HTTP Server 8.5 and 9.0 are vulnerable to denial of service when an attacker has write access to server configuration files. The vulnerability stems from uncontrolled resource consumption (CWE-400) and can be exploited locally with low complexity. Successful exploitation results in high impact to system integrity and availability. The attack requires no privileges or user interaction from the attacker's perspective, though write access to configuration files implies some level of system access has already been obtained. IBM has released fix packs addressing this issue.

Defensive priority

HIGH

Recommended defensive actions

  • Apply IBM HTTP Server fix packs 8.5.5.30 or later, or 9.0.5.29 or later, as detailed in the vendor security advisory.
  • Restrict write access to IBM HTTP Server configuration files (httpd.conf and included configuration files) to authorized administrative accounts only.
  • Audit file system permissions on IBM HTTP Server configuration directories to ensure no unauthorized write access exists.
  • Monitor for unexpected modifications to server configuration files as an indicator of potential exploitation attempts.
  • Review and implement principle of least privilege for all accounts with access to IBM HTTP Server installation and configuration directories.

Evidence notes

The vulnerability affects IBM HTTP Server 8.5.0.0 through 8.5.5.29 and 9.0.0.0 through 9.0.5.28. The CPE data indicates the software runs on AIX, z/OS, Linux, and Windows platforms, though the operating systems themselves are not vulnerable.

Official resources

IBM disclosed this vulnerability via their Product Security Incident Response Team (PSIRT) and it was subsequently published in the NVD on 2026-05-26.