CVE-2025-55315Public exploitNetwork attack vector

Security control bypass via chunk-extension request smuggling

Published Oct 14, 2025 · Updated Oct 14, 2025

HTTP request smuggling in Microsoft ASP.NET Core 2.3, 8.0, and 9.0 allows remote authenticated users to bypass security controls. Kestrel incorrectly parses crafted HTTP chunk extensions, causing its request boundaries to differ from those recognized by a front-end proxy. Exploitation requires network access, low privileges, and an intermediary with divergent parsing; a hidden request can then reach a protected endpoint.

CVSS severity9.9
Critical
EPSS probability65.94%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in Microsoft ASP.NET Core 2.3, 8.0, and 9.0 allows remote authenticated users to bypass security controls. Kestrel incorrectly parses crafted HTTP chunk extensions, causing its request boundaries to differ from those recognized by a front-end proxy. Exploitation requires network access, low privileges, and an intermediary with divergent parsing; a hidden request can then reach a protected endpoint.

The record

CVE
CVE-2025-55315
Published
Oct 14, 2025
Updated
Oct 14, 2025
Vendor
Microsoft
Product
ASP.NET Core 8.0
Classifications
T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 14, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 14, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=8.0 <8.0.21

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Microsoft · ASP.NET Core 8.0version=8.0 <8.0.21
Microsoft · ASP.NET Core 9.0version=9.0 <9.0.10
Microsoft · Microsoft Visual Studio 2022 version 17.10version=17.10.0 <17.10.20
Microsoft · Microsoft Visual Studio 2022 version 17.12version=17.12.0 <17.12.13
Microsoft · Microsoft Visual Studio 2022 version 17.14version=17.14.0 <17.14.17
Microsoft · ASP.NET Coreversion=2.3 <2.3.6

Published CVSS scores

9.9MicrosoftCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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