CVE-2025-58068: Eventlet Auth Bypass Vulnerability

CVE-2025-58068 Overview

CVE-2025-58068 is an HTTP Request Smuggling vulnerability in Eventlet, a concurrent networking library for Python. The vulnerability exists in the Eventlet WSGI parser due to improper handling of HTTP trailer sections. This flaw could enable attackers to bypass front-end security controls, launch targeted attacks against active site users, and poison web caches.

Critical Impact

Attackers can exploit improper HTTP trailer handling to smuggle malicious requests past front-end security controls, potentially leading to cache poisoning and targeted attacks against users.

Affected Products

• Eventlet versions prior to 0.40.3
• Applications using eventlet.wsgi facing untrusted clients
• Web services with Eventlet-based WSGI proxy configurations

Discovery Timeline

• 2025-08-29 - CVE-2025-58068 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-58068

Vulnerability Analysis

This vulnerability is classified as CWE-444 (Inconsistent Interpretation of HTTP Requests). The Eventlet WSGI parser fails to properly handle HTTP trailer sections in chunked transfer encoding. HTTP trailers are headers sent after the message body in chunked transfers, and when improperly processed, they can be interpreted differently by front-end proxies and back-end servers.

The core issue stems from the parser not discarding trailer sections, allowing attackers to craft requests where the trailer content gets interpreted as the beginning of a new HTTP request by the back-end server. This desynchronization between how front-end and back-end systems interpret the HTTP message boundaries is the essence of HTTP Request Smuggling.

Root Cause

The Eventlet WSGI parser did not implement proper handling for HTTP trailer sections in chunked transfer-encoded requests. Without explicit trailer discarding logic, the parser could pass trailer data through in a way that causes request boundary confusion. The fix introduces a _discard_trailers() method that properly reads and discards all trailer lines until an empty line is encountered.

Attack Vector

This vulnerability is exploitable over the network without authentication. An attacker sends specially crafted HTTP requests with malicious content in the trailer section. Due to the inconsistent parsing, the front-end proxy sees one complete request while the back-end Eventlet server may interpret the trailer content as part of a subsequent request. This enables:

1. Security Control Bypass - Smuggled requests bypass front-end WAF rules and access controls
2. Cache Poisoning - Attackers can inject malicious responses into cache entries for legitimate URLs
3. Request Hijacking - Active user sessions can be targeted by injecting requests into their connection

# Security patch - _discard_trailers method added to properly handle trailer sections
# Source: https://github.com/eventlet/eventlet/commit/0bfebd1117d392559e25b4bfbfcc941754de88fb

             read = b''
         self.position += len(read)
         return read
+    
+    def _discard_trailers(self, rfile):
+        while True:
+            line = rfile.readline()
+            if not line or line in (b'\r\n', b'\n', b''):
+                break
 
     def _chunked_read(self, rfile, length=None, use_readline=False):
         if self.should_send_hundred_continue:

Detection Methods for CVE-2025-58068

Indicators of Compromise

• Unusual HTTP requests with oversized or malformed trailer sections in chunked transfer-encoded requests
• Discrepancies between front-end proxy logs and back-end server request logs
• Unexpected cache entries or cache behavior anomalies
• Reports of users receiving content intended for other users

Detection Strategies

• Monitor for chunked transfer-encoded requests with suspicious trailer content patterns
• Implement HTTP request logging at both proxy and application layers to detect parsing inconsistencies
• Deploy web application firewall rules to detect HTTP request smuggling attempts
• Analyze access logs for requests that appear to bypass authentication or authorization controls

Monitoring Recommendations

• Enable detailed HTTP request logging including headers and chunked encoding metadata
• Set up alerts for anomalous patterns in request sizes or trailer section presence
• Monitor cache hit/miss ratios for unexpected changes that could indicate poisoning
• Track error rates for HTTP parsing failures which may indicate exploitation attempts

How to Mitigate CVE-2025-58068

Immediate Actions Required

• Upgrade Eventlet to version 0.40.3 or later immediately
• Audit applications using eventlet.wsgi to identify exposure to untrusted clients
• Review recent access logs for signs of HTTP request smuggling attempts
• Consider implementing additional front-end filtering for chunked transfer-encoded requests

Patch Information

The vulnerability has been patched in Eventlet version 0.40.3. The fix discards HTTP trailers, which is a breaking change for backends that require trailer support behind an eventlet.wsgi proxy. The patch commit is available at the GitHub Commit. Additional details are provided in the GitHub Security Advisory.

Workarounds

• Avoid using eventlet.wsgi when handling requests from untrusted clients
• Place a reverse proxy that normalizes HTTP requests before they reach Eventlet
• Implement request validation at the application layer to reject suspicious chunked requests
• Consider using alternative WSGI servers that properly handle trailer sections

# Upgrade Eventlet to patched version
pip install --upgrade eventlet>=0.40.3

# Verify installed version
pip show eventlet | grep Version