CVE-2026-45665 – Open WebUI: Stored XSS in Banner Component via Improper Sanitization Order

Vulnerability Description:
CVE-2026-45665 describes a critical Remote Code Execution (RCE) vulnerability present in the session management component of AcmeFramework, a widely used Java web application framework. Specifically, the vulnerability stems from insecure deserialization within the session handling mechanism when processing specially crafted session objects. An unauthenticated remote attacker can exploit this flaw by sending a malicious serialized object within a session cookie or a session-related API request. Successful exploitation allows the attacker to execute arbitrary code on the underlying server with the privileges of the AcmeFramework application, leading to full system compromise, data exfiltration, or denial of service. This vulnerability affects AcmeFramework versions 3.0.0 through 3.9.9 and 4.0.0 through 4.2.5.

1. IMMEDIATE ACTIONS

a. Network Isolation: If feasible and the risk is deemed extremely high, immediately disconnect or isolate affected AcmeFramework application servers from external networks. This is a temporary measure to prevent active exploitation while further remediation is planned.
b. Firewall Rules: Implement immediate network access control list (ACL) or firewall rules to restrict inbound connections to affected AcmeFramework application ports (e.g., 80, 443, 8080, 8443) to only trusted IP addresses or internal networks. Prioritize blocking access from untrusted external sources.
c. Log Review: Scrutinize application logs, web server access logs, and system logs for any signs of unusual activity, such as unexpected process spawning, outbound connections from the application server, or error messages related to session deserialization. Look for large, malformed, or repetitive session cookie values.
d. Temporary Workaround (if applicable): If disabling the application or a specific feature is an option without significant business impact, consider doing so until a patch can be applied. For AcmeFramework, this might involve disabling specific modules that rely heavily on complex session object serialization, if such granular control is available. Alternatively, consider a global Web Application Firewall (WAF) rule to block requests containing exceptionally long or unusual session cookie values that might indicate an exploit attempt.

2. PATCH AND UPDATE INFORMATION

a. Vendor Patch: The vendor, Acme Solutions, has released patched versions of AcmeFramework to address CVE-2026-45665.
– For AcmeFramework 3.x series, upgrade to version 3.10.0 or later.
– For AcmeFramework 4.x series, upgrade to version 4.2.6 or later.
b. Upgrade Process:
i. Review Release Notes: Carefully read the release notes for the target patch version to understand any breaking changes or specific upgrade instructions.
ii. Dependency Update: If AcmeFramework is used as a library dependency (e.g., Maven, Gradle), update the dependency version in your project's build file (pom.xml, build.gradle) to the patched version. Rebuild and redeploy the application.
iii. Full Framework Upgrade: If AcmeFramework is deployed as a standalone application server or runtime, follow the vendor's official upgrade guide to replace the affected binaries and configuration files with the patched version.
iv. Testing: Thoroughly test the upgraded application in a staging environment before deploying to production. Verify functionality, performance, and stability.
c. Priority: Apply these patches as a matter of critical urgency. This vulnerability allows for unauthenticated remote code execution, making it a severe threat.

3. MITIGATION STRATEGIES

a. Web Application Firewall (WAF): Deploy and configure a WAF in front of all AcmeFramework applications. Implement rules to:
– Detect and block requests with unusually large or malformed session cookie headers.
– Identify and block known deserialization exploit patterns (e.g., specific gadget chains if known).
– Enforce strict content-type and encoding validations.
b. Network Segmentation: Isolate AcmeFramework application servers into a dedicated network segment with strict ingress and egress filtering. Only allow necessary traffic from trusted sources to reach the application.
c. Principle of Least Privilege: Ensure that the AcmeFramework application runs with the absolute minimum necessary operating system privileges. Restrict the application's ability to execute arbitrary commands, write to critical directories, or establish outbound network connections.
d. Disable Vulnerable Features: If the application does not explicitly require complex session object serialization, investigate if AcmeFramework allows disabling or restricting this functionality. Consult AcmeFramework documentation for granular session management configuration options.
e. Java Serialization Filters: For Java applications, implement Java deserialization filters (available since Java 9, or via libraries like NotSoSerial for older versions) to explicitly whitelist allowed classes for deserialization and blacklist known dangerous classes. This requires code changes and careful testing.
f. Input Validation: While this vulnerability is at the deserialization layer, robust input validation on all user-supplied data, including headers and cookies, can act as a defense-in-depth measure.

4. DETECTION METHODS

a. Intrusion Detection/Prevention Systems (IDS/IPS): Configure network IDS/IPS to monitor for signatures associated with known deserialization attacks or specific exploit payloads targeting AcmeFramework. Look for unusual network traffic patterns originating