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HTTP ServerWeb server / proxy · Ibm

CVE-2026-8855

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-26
Fix available
A fix is available. Upgrade to 8.5.5.30 / 9.0.5.29 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
IBM HTTP Server 8.5, and 9.0 is vulnerable to remote code execution and denial of service in configurations with TLS mutual authentication (client authentication).

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

IBM HTTP Server versions 8.5 and 9.0 contains a critical vulnerability when configured with TLS mutual authentication (client certificate authentication). The vulnerability allows remote attackers to execute arbitrary code or cause denial of service via the mutual TLS handshake mechanism. The CVSS 9.8 score indicates trivial exploitability with network-based attacks achieving code execution.

MitigationDisable TLS mutual authentication if not operationally required, or apply IBM-supplied patches for this vulnerability. Review TLS configuration to ensure client certificate validation is properly implemented if mutual auth is necessary.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
HTTP ServerWeb server / proxy
Affected:>= 8.5.0.0, < 8.5.5.30>= 9.0.0.0, < 9.0.5.29

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed IBM HTTP Server version
    Run 'lsitab ihs' or check the version using the 'gskcmd' utility (e.g., gskcmd -version) or inspect the binary at /opt/IBM/HTTPServer/bin/httpd -v
    Affected if The installed version falls within 8.5.0.0 - 8.5.5.29 or 9.0.0.0 - 9.0.5.28
  2. Verify if TLS mutual authentication is enabled
    Search the IBM HTTP Server configuration files (httpd.conf, plugin-cfg.xml) for the 'SSLVerifyClient' directive. If set to 'required' or 'optional', mutual TLS is enabled. Also check for 'SSLRequire' directives that enforce client certificate validation.
    Affected if SSLVerifyClient is set to 'required' or 'optional', enabling client certificate authentication
  3. Check Listen directives for SSL-enabled ports
    Review the httpd.conf for 'Listen' statements on SSL ports (typically 443 or custom ports) and verify they are associated with an SSLSocket or SSL-enabled virtual host configuration.
    Affected if SSL-enabled listeners are configured, which is a prerequisite for mutual TLS to function
  4. Inspect client certificate validation rules
    Examine any 'SSLRequire' directives or custom client certificate validation logic in the configuration. Look for rules that accept client certificates without strict validation patterns.
    Affected if Client certificates are accepted without strict validation rules or the validation logic can be bypassed

A system is affected if it runs IBM HTTP Server 8.5.0.0-8.5.5.29 or 9.0.0.0-9.0.5.28 AND has TLS mutual authentication (SSLVerifyClient) enabled in the configuration.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 8.5.5.30 / 9.0.5.29 or later
Fixed in 8.5.5.309.0.5.29
Interim mitigation

Disable TLS mutual authentication if not operationally required, or apply IBM-supplied patches for this vulnerability. Review TLS configuration to ensure client certificate validation is properly implemented if mutual auth is necessary.

Recommended fix High confidence

IBM HTTP Server 8.5.5.30 or 9.0.5.29

  1. Identify the currently installed IBM HTTP Server version using the 'apachectl -v' or 'httpd -v' command
  2. Backup your current IBM HTTP Server configuration, including httpd.conf and any included configuration files
  3. Download IBM HTTP Server fix pack 8.5.5.30 (for 8.5.x installations) or 9.0.5.29 (for 9.0.x installations) from IBM Fix Central (https://www.ibm.com/support/fixcentral)
  4. Stop the IBM HTTP Server service using 'apachectl stop' or the appropriate service management command for your operating system
  5. Install the downloaded fix pack following IBM's standard installation procedures for HTTP Server fix packs
  6. Verify the installation was successful by checking the new version with 'apachectl -v' or 'httpd -v'
  7. Start the IBM HTTP Server service using 'apachectl start' or the appropriate service management command
  8. Test that applications served by the HTTP Server are functioning correctly
Caveat Review IBM HTTP Server fix pack release notes for any changes to configuration defaults or deprecated features before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in HTTP Server Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,840
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-8855 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data