CVE-2025-12811: Delinea Server Suite HTTP Smuggling Flaw

CVE-2025-12811 Overview

CVE-2025-12811 is an HTTP Request Smuggling vulnerability (CWE-444) affecting Delinea Inc. Cloud Suite and Privileged Access Service. This vulnerability arises from improper inconsistent interpretation of HTTP requests, allowing attackers to potentially bypass security controls, poison web caches, or hijack user sessions by exploiting discrepancies in how front-end and back-end servers process HTTP requests.

Critical Impact

Attackers can exploit this HTTP Request Smuggling vulnerability to bypass security controls, access unauthorized resources, or conduct session hijacking attacks against privileged access management infrastructure.

Affected Products

• Delinea Cloud Suite (versions prior to 25.1)
• Delinea Privileged Access Service
• Server Suite agents prior to version 6.0.1

Discovery Timeline

• 2026-02-18 - CVE-2025-12811 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2025-12811

Vulnerability Analysis

This HTTP Request Smuggling vulnerability occurs when the Delinea Cloud Suite and Privileged Access Service improperly interpret HTTP requests in an inconsistent manner between different components of the request processing chain. HTTP Request Smuggling exploits differences in how front-end servers (such as load balancers, reverse proxies, or CDNs) and back-end servers parse HTTP request boundaries.

The vulnerability is accessible via network attack vector and requires no authentication or user interaction to exploit, making it particularly concerning for internet-facing deployments. Successful exploitation could allow attackers to smuggle malicious requests through security controls, gaining unauthorized access to protected resources or interfering with other users' sessions.

Root Cause

The root cause of CVE-2025-12811 lies in the inconsistent interpretation of HTTP request boundaries between different components in the request processing pipeline. This typically occurs due to ambiguities in how Content-Length and Transfer-Encoding headers are handled, or discrepancies in parsing chunked encoding. When front-end and back-end servers disagree on where one request ends and another begins, attackers can craft specially formatted requests that are interpreted differently by each server, allowing malicious payload injection.

Attack Vector

HTTP Request Smuggling attacks against this vulnerability would involve an attacker sending a specially crafted HTTP request to the affected Delinea service. The malicious request exploits parsing differences to "smuggle" a secondary request that bypasses security controls. This can be achieved through:

1. CL.TE (Content-Length/Transfer-Encoding): Sending conflicting Content-Length and Transfer-Encoding headers where the front-end uses Content-Length and the back-end uses Transfer-Encoding
2. TE.CL: The reverse scenario where the front-end uses Transfer-Encoding and the back-end uses Content-Length
3. TE.TE: Both servers support Transfer-Encoding but can be induced to process it differently through obfuscation

The attacker does not require any privileges or authentication to attempt exploitation, as the vulnerability exists in the HTTP parsing layer before authentication occurs.

Detection Methods for CVE-2025-12811

Indicators of Compromise

• Unusual HTTP requests containing conflicting Content-Length and Transfer-Encoding headers
• Malformed chunked encoding in HTTP request bodies targeting Delinea services
• Unexpected request patterns or duplicate requests appearing in back-end server logs
• Session anomalies or unauthorized access attempts following suspicious HTTP traffic

Detection Strategies

• Deploy web application firewalls (WAF) with HTTP Request Smuggling detection rules to identify malformed requests
• Implement deep packet inspection on traffic destined for Delinea Cloud Suite endpoints
• Monitor for requests containing both Content-Length and Transfer-Encoding headers simultaneously
• Enable verbose logging on front-end proxies and back-end servers to correlate request discrepancies

Monitoring Recommendations

• Configure alerting for HTTP parsing errors or rejected requests at load balancers and reverse proxies
• Establish baseline traffic patterns for Delinea services and alert on anomalies
• Review access logs for unauthorized resource access attempts that may indicate successful smuggling
• Monitor authentication and session logs for signs of session hijacking

How to Mitigate CVE-2025-12811

Immediate Actions Required

• Upgrade to Server Suite 2023.1 (agent version 6.0.1) or later immediately
• If unable to upgrade to the latest version, apply Server Suite release 2023.0.5 (agent version 6.0.0-158) or Server Suite release 2022.1.10 (agent version 5.9.1-337)
• Review the Delinea Cloud Suite Release Notes for complete upgrade instructions
• Consult the Delinea Trust Center for additional security guidance

Patch Information

Delinea has released patches addressing CVE-2025-12811 in multiple versions to accommodate different deployment scenarios:

Organizations should prioritize upgrading to the latest Server Suite 2023.1 release with agent version 6.0.1 or later for the most comprehensive fix.

Workarounds

• Deploy a properly configured reverse proxy or WAF that normalizes HTTP requests before forwarding to Delinea services
• Configure front-end servers to reject ambiguous requests containing both Content-Length and Transfer-Encoding headers
• Implement strict HTTP parsing rules that reject malformed chunked encoding
• Consider network segmentation to limit exposure of affected services while patching is in progress
• Enable HTTP/2 end-to-end where supported, as HTTP Request Smuggling typically exploits HTTP/1.1 parsing ambiguities

# Example WAF rule to reject ambiguous requests (conceptual)
# Block requests with both Content-Length and Transfer-Encoding headers
# Implementation varies by WAF vendor

# For nginx, consider adding:
# proxy_http_version 1.1;
# proxy_set_header Connection "";

# Ensure consistent HTTP parsing between proxy and backend