CVE-2004-0847
CriticalExploitedPublic exploitThe Microsoft .NET forms authentication capability for ASP.NET allows remote attackers to bypass authentication for .aspx files in restricted directories via a request containing a (1) "\" (backslash) or (2) "%5C" (encoded backslash), aka "Path Validation Vulnerability."
Published Nov 3, 2004 · Updated Apr 15, 2026
Key Facts
Patch immediately- CVE-2004-0847 is a critical-severity vulnerability (CVSS 9.8 v3) affecting Asp.net (Microsoft).
- It is exploited in the wild, listed in Industry KEV feed since Feb 8, 2005. Public exploit code is available.
- EPSS estimates a 76% probability of exploitation in the next 30 days.
- Fixed versions are available, including Asp.net 1.1.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3
9.8
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
76%
Higher than 99.5% of all scored CVEs
Exploited in the wild
Yes
1 catalog listing
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2004-0847 brief as a PDF
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Description
The Microsoft .NET forms authentication capability for ASP.NET allows remote attackers to bypass authentication for .aspx files in restricted directories via a request containing a (1) "\" (backslash) or (2) "%5C" (encoded backslash), aka "Path Validation Vulnerability."
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| Industry KEV feed | Feb 8, 2005 | n/a | Not reported |
Required action: Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable.
Affected Products
2 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Asp.netMicrosoft | 1.1-sp1 | 1.1 |
Patched Releases
Asp.net
1.1
Timeline
Publicly disclosed
Nov 3, 2004
Added to Industry KEV feed
Feb 8, 2005
Last updated
Apr 15, 2026
Weakness Type
- CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
References
- advisorywindows-forms-security-bypass(17644)
- advisoryoval:org.mitre.oval:def:3556
- advisoryoval:org.mitre.oval:def:4987
- advisoryVU#283646
- advisory11342
FAQ
Common Questions.
The Microsoft .NET forms authentication capability for ASP.NET allows remote attackers to bypass authentication for .aspx files in restricted directories via a request containing a (1) "\" (backslash) or (2) "%5C" (encoded backslash), aka "Path Validation Vulnerability."
Affected: Asp.net (Microsoft) versions 1.1-sp1. The full list is in the CVE brief.
It is exploited in the wild, listed in Industry KEV feed since Feb 8, 2005.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
Public exploit code is available.
Fixed versions are available, including Asp.net 1.1.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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