CVE-2025-55315: Microsoft Security Advisory CVE-2025-55315: .NET Security Feature Bypass Vulnerability

Should you act?

High exploit likelihood

EPSS ranks it in the top 5% of all CVEs for likely exploitation in the next 30 days. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 66.5%, percentile 99: FIRST’s model estimates a 66.5% chance of exploitation activity in the next 30 days, higher than 99% of all scored CVEs (very high). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes Microsoft.AspNetCore.App.Runtime.linux-arm (NuGet) = 10.0.0-rc.1.25451.107, fixed in 10.0.0-rc.2.25502.107; Microsoft.AspNetCore.App.Runtime.linux-arm64 (NuGet) = 10.0.0-rc.1.25451.107, fixed in 10.0.0-rc.2.25502.107; Microsoft.AspNetCore.App.Runtime.linux-musl-arm (NuGet) = 10.0.0-rc.1.25451.107, fixed in 10.0.0-rc.2.25502.107; Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 (NuGet) = 10.0.0-rc.1.25451.107, fixed in 10.0.0-rc.2.25502.107. Check your lockfile, including transitive dependencies.

What it is

Inconsistent interpretation of http requests ('http request/response smuggling') in ASP.NET Core allows an authorized attacker to bypass a security feature over a network.

From the GitHub advisory

Microsoft Security Advisory CVE-2025-55315: .NET Security Feature Bypass Vulnerability

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core 10.0 , ASP.NET Core 9.0 , ASP.NET Core 8.0, and ASP.NET Core 2.3. This advisory also provides guidance on what developers can do to update their applications to address this vulnerability.

Inconsistent interpretation of http requests ('http request/response smuggling') in ASP.NET Core allows an authorized attacker to bypass a security feature over a network.

Discussion

Weakness type: CWE-444.

Product: Microsoft.AspNetCore.App.Runtime.linux-arm (NuGet) · Assigned by: microsoft · Published: 2025-10-14

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 66.53% probability of exploitation activity in the next 30 days; percentile 99.

Timeline

• 2025-10-14 — CVE record published by microsoft
• 2025-10-14 — GitHub-reviewed advisory GHSA-5rrx-jjjq-q2r5 published (critical)
• 2026-02-22 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. ASP.NET Security Feature Bypass Vulnerability msrc.microsoft.com

Vulnerability records

1. GitHub Advisory GHSA-5rrx-jjjq-q2r5 github.com
2. CVE.org record CVE-2025-55315 cve.org
3. NVD entry CVE-2025-55315 nvd.nist.gov

Other references from the CVE record and advisory

1. gist.github.com gist.github.com
2. andrewlock.net andrewlock.net
3. github.com github.com
4. github.com github.com

Critical NuGet advisories · Today’s Security Digest