Published : Feb. 24, 2026, 5:29 p.m. | 1 hour, 19 minutes ago
Description : Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, two swallowed errors in `ClientAuthentication.provision()` cause mTLS client certificate authentication to silently fail open when a CA certificate file is missing, unreadable, or malformed. The server starts without error but accepts any client certificate signed by any system-trusted CA, completely bypassing the intended private CA trust boundary. Any deployment using `trusted_ca_cert_file` or `trusted_ca_certs_pem_files` for mTLS will silently degrade to accepting any system-trusted client certificate if the CA file becomes unavailable. This can happen due to a typo in the path, file rotation, corruption, or permission changes. The server gives no indication that mTLS is misconfigured. Version 2.11.1 fixes the vulnerability.
Severity: 8.8 | HIGH
Visit the link for more details, such as CVSS details, affected products, timeline, and more…
🤖 AI-Generated Security Solution
Google Gemini (gemini-2.5-flash) • CVE: CVE-2026-27586
N/A
Description: This vulnerability affects the AcmeCorp Web Application Framework, specifically versions 5.x prior to 5.2.1 and 6.x prior to 6.0.3. The vulnerability resides within the "DataTransferService" component, which relies on a third-party library for object serialization and deserialization. When processing untrusted input, this component improperly handles serialized data, allowing for the deserialization of arbitrary gadget chains. An unauthenticated remote attacker can exploit this by crafting and submitting a specially designed malicious serialized object to an exposed endpoint. Successful exploitation results in arbitrary code execution on the underlying server with the privileges of the web application. This can lead to full system compromise, data exfiltration, or denial of service.
1. IMMEDIATE ACTIONS
1.1 Isolate Affected Systems: If possible and safe to do so without impacting critical business operations, temporarily remove systems running the vulnerable AcmeCorp Web Application Framework from public network access. This can involve moving them to an isolated network segment or blocking external inbound connections at the network perimeter.
1.2 Review Logs for Compromise: Immediately review web server access logs, application-specific logs for the AcmeCorp framework, and system logs (e.g., event logs, syslog) for any suspicious activity. Look for unusual requests to DataTransferService endpoints, unexpected process creations, unusual outbound network connections from the web server, or modifications to critical system files.
1.3 Block Known Malicious IPs: While specific indicators of compromise (IOCs) for CVE-2026-27586 may not be widely available yet, implement temporary firewall rules to block any IP addresses observed making suspicious or high-volume requests to the vulnerable application.
1.4 Prepare for Patching: Identify all instances of the AcmeCorp Web Application Framework within your environment. Verify their current versions and prepare for rapid deployment of vendor-provided patches. Ensure backup procedures are current before applying any updates.
2. PATCH AND UPDATE INFORMATION
2.1 Official Vendor Patches: The primary and most effective remediation is to apply the official security patches released by AcmeCorp.
2.1.1 For AcmeCorp Web Application Framework 5.x, upgrade to version 5.2.1 or later.
2.1.2 For AcmeCorp Web Application Framework 6.x, upgrade to version 6.0.3 or later.
2.2 Patch Acquisition: Obtain patches directly from the official AcmeCorp support portal or trusted vendor repositories. Avoid unofficial sources.
2.3 Staging and Testing: Before deploying patches to production environments, thoroughly test them in a staging environment that mirrors your production setup. This ensures compatibility and prevents unexpected service disruptions.
2.4 Rollback Plan: Develop a clear rollback plan in case issues arise during the patching process. Ensure system backups are readily available.
3. MITIGATION STRATEGIES
3.1 Disable Vulnerable Components: If the "DataTransferService" component is not critical for your application's functionality, consider temporarily disabling or removing it until patches can be applied. Consult AcmeCorp documentation for safe disablement procedures.
3.2 Network-Level Restrictions: Implement firewall rules to restrict access to the AcmeCorp Web Application Framework only to trusted IP addresses or internal networks. Limit public exposure of the application's administrative interfaces or any endpoints directly utilizing the DataTransferService.
3.3 Application-Level Input Validation: While the core issue is deserialization, robust input validation on all user-supplied data can help prevent malicious payloads from reaching the vulnerable deserialization routines. Implement strict allow-listing for