‘Highest Ever’ Severity Score Assigned by Microsoft to ASP.NET Core Vulnerability
Source SecurityWeek
Not known to be exploited · public exploit available (Exploit-DB) · CVSS 9.9 Critical.
Data as of 20 Oct 2025, 01:36 UTC
Exploitation evidence
t = 0 is the CVE’s publication on cve.org
Disclosed: evidence found.
CVE published 14 Oct 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: evidence found.
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
Timeline
CVE ID reserved
by microsoft
, 63 days before disclosure
CVE published
on cve.org
, t = 0
In Threat Radar
record ingested
, 17 minutes after disclosure
First Exploit-DB entry (opens in a new tab)
ASP.net 8.0.10 - Bypass
, 174 days after disclosure
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.
What to do
AI-suggested
Organizations should prioritize the following mitigations: 1) Monitor Microsoft advisories closely and apply security patches for ASP.NET Core as soon as they are released. 2) Implement strict input validation and HTTP header inspection at web application firewalls (WAFs) and reverse proxies to detect and block malformed or suspicious HTTP requests indicative of request smuggling attempts. 3) Employ layered security controls such as network segmentation and least privilege to limit the impact of potential breaches. 4) Conduct thorough security testing, including fuzzing and penetration testing, focusing on HTTP request parsing and handling. 5) Enable detailed logging and monitoring of HTTP traffic to identify anomalies early. 6) Educate development and operations teams about the risks of HTTP request smuggling and secure coding practices. These steps go beyond generic patching by emphasizing proactive detection and defense-in-depth strategies.
Description
CVE-2025-55315 is an HTTP request smuggling bug leading to information leaks, file content tampering, and server crashes. The post ‘Highest Ever’ Severity Score Assigned by Microsoft to ASP.NET Core Vulnerability appeared first on SecurityWeek .