What is CVE-2025-57804?

CVE-2025-57804 is a medium-severity security vulnerability in h2 (pip), affecting versions < 4.3.0. It is fixed in 4.3.0.

Which versions of h2 are affected by CVE-2025-57804?

h2 (pip) versions < 4.3.0 is affected.

Is there a fix for CVE-2025-57804?

Yes. CVE-2025-57804 is fixed in 4.3.0. Upgrade to this version or later.

Is CVE-2025-57804 exploitable, and should I be worried?

Whether CVE-2025-57804 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk.

What actually determines whether CVE-2025-57804 is exploitable, and how bad it is?

Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.

CVE-2025-57804 in h2

Q: Which versions of h2 are affected by CVE-2025-57804?

h2 (pip) versions < 4.3.0 is affected.

Q: Is there a fix for CVE-2025-57804?

Yes. CVE-2025-57804 is fixed in 4.3.0. Upgrade to this version or later.

Q: Is CVE-2025-57804 exploitable, and should I be worried?

Whether CVE-2025-57804 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk.

Q: What actually determines whether CVE-2025-57804 is exploitable, and how bad it is?

Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.

Summary

h2 allows HTTP Request Smuggling due to illegal characters in headers

HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls.

Impact

Affected versions

h2 (< 4.3.0)

Security releases

h2 → 4.3.0 (pip)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

Upgrade h2 to 4.3.0 or later to resolve this vulnerability.

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

What is CVE-2025-57804? CVE-2025-57804 is a medium-severity security vulnerability in h2 (pip), affecting versions < 4.3.0. It is fixed in 4.3.0.
Which versions of h2 are affected by CVE-2025-57804? h2 (pip) versions < 4.3.0 is affected.
Is there a fix for CVE-2025-57804? Yes. CVE-2025-57804 is fixed in 4.3.0. Upgrade to this version or later.
Is CVE-2025-57804 exploitable, and should I be worried? Whether CVE-2025-57804 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
What actually determines whether CVE-2025-57804 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
How do I fix CVE-2025-57804? Upgrade h2 to 4.3.0 or later.

Other vulnerabilities in h2

CVE-IDSeverityPackage summary

GHSA-Q6CP-QFWQ-4GCVMediumh2: h2 servers vulnerable to degradation of service with CONTINUATION Flood GHSA-8R5V-VM4M-4G25Mediumh2: Resource exhaustion vulnerability in h2 may lead to Denial of Service (DoS)CVE-2023-26964Mediumh2: h2 vulnerable to denial of service