CVE-2025-55315
📋 TL;DR
CVE-2025-55315 is an HTTP request smuggling vulnerability in ASP.NET Core that allows an authenticated attacker to bypass security features by manipulating HTTP request/response sequences. This affects ASP.NET Core applications that process HTTP traffic, potentially enabling privilege escalation or data exposure.
💻 Affected Systems
- ASP.NET Core
📦 What is this software?
Asp.net Core by Microsoft
Asp.net Core by Microsoft
Asp.net Core by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise via privilege escalation to admin, data exfiltration, or remote code execution through bypassed security controls.
Likely Case
Unauthorized access to restricted endpoints, data leakage from other user sessions, or bypassing authentication/authorization mechanisms.
If Mitigated
Limited impact due to defense-in-depth controls, with potential for some request manipulation but contained by additional security layers.
🎯 Exploit Status
Exploitation requires understanding of HTTP protocol manipulation and authenticated access. Public proof-of-concept demonstrates the technique.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: ASP.NET Core 8.0.10 and 7.0.23
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-55315
Restart Required: Yes
Instructions:
1. Update to ASP.NET Core 8.0.10 or 7.0.23 via NuGet package manager. 2. Update runtime if using self-contained deployment. 3. Restart application/services. 4. Test functionality after update.
🔧 Temporary Workarounds
HTTP/2 Disable
allDisable HTTP/2 protocol to reduce attack surface (HTTP/1.1 still vulnerable but may limit some attack vectors)
In Program.cs: builder.WebHost.ConfigureKestrel(options => options.ConfigureEndpointDefaults(lo => lo.Protocols = HttpProtocols.Http1))
Reverse Proxy Configuration
allConfigure reverse proxy (nginx, Apache, IIS) to normalize HTTP requests and prevent smuggling attempts
nginx: proxy_http_version 1.1; proxy_set_header Connection "";
IIS: Set URL Rewrite rules to reject malformed requests
🧯 If You Can't Patch
- Implement strict input validation and request normalization at application layer
- Deploy WAF with HTTP request smuggling protection rules enabled
🔍 How to Verify
Check if Vulnerable:
Check ASP.NET Core version via 'dotnet --info' or examine project dependencies in .csproj files for versions <8.0.10 or <7.0.23Check Version:
dotnet --info | findstr "Version"Verify Fix Applied:
Confirm version is 8.0.10+ or 7.0.23+ via 'dotnet --info' and test with known proof-of-concept requests📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP request patterns with Content-Length/Transfer-Encoding discrepancies
- 401/403 errors followed by successful requests from same source
- Requests with malformed headers or chunked encoding anomalies
Network Indicators:
- HTTP traffic with inconsistent Content-Length and Transfer-Encoding headers
- Requests that appear to be split across multiple packets abnormally
SIEM Query:
(http.request.method AND (http.header.content-length OR http.header.transfer-encoding)) | stats count by src_ip, http.request.uri