When a server is configured to support unencrypted HTTP/2, it reads a few bytes from each new connection to see if they contain the HTTP/2 client… (CVE-2026-56853)
CVE-2026-56853 is a vulnerability affecting servers configured to support unencrypted HTTP/2 connections. The server reads initial bytes from each new connection to detect the HTTP/2 client preface, but the ReadHeaderTimeout setting is not applied during this process. This can lead to a denial of service condition due to resource exhaustion.
AI Analysis
Technical Summary
When a server supports unencrypted HTTP/2, it inspects the first few bytes of each new connection to identify the HTTP/2 client preface. However, the ReadHeaderTimeout, which limits the time allowed to read the request headers, is not enforced during this initial read. This flaw can be exploited to keep connections open indefinitely, potentially exhausting server resources and causing a denial of service. The vulnerability is tracked as CVE-2026-56853 and is associated with CWE-770 (Allocation of Resources Without Limits or Throttling).
Potential Impact
The vulnerability allows an attacker to cause a denial of service by exploiting the lack of timeout enforcement during the initial read of HTTP/2 client preface bytes on unencrypted connections. This can lead to resource exhaustion on the affected server, impacting availability.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, consider disabling unencrypted HTTP/2 support or applying network-level protections to limit connection attempts.
When a server is configured to support unencrypted HTTP/2, it reads a few bytes from each new connection to see if they contain the HTTP/2 client… (CVE-2026-56853)
Description
CVE-2026-56853 is a vulnerability affecting servers configured to support unencrypted HTTP/2 connections. The server reads initial bytes from each new connection to detect the HTTP/2 client preface, but the ReadHeaderTimeout setting is not applied during this process. This can lead to a denial of service condition due to resource exhaustion.
CVSS v3.1
Score 7.5high
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
When a server supports unencrypted HTTP/2, it inspects the first few bytes of each new connection to identify the HTTP/2 client preface. However, the ReadHeaderTimeout, which limits the time allowed to read the request headers, is not enforced during this initial read. This flaw can be exploited to keep connections open indefinitely, potentially exhausting server resources and causing a denial of service. The vulnerability is tracked as CVE-2026-56853 and is associated with CWE-770 (Allocation of Resources Without Limits or Throttling).
Potential Impact
The vulnerability allows an attacker to cause a denial of service by exploiting the lack of timeout enforcement during the initial read of HTTP/2 client preface bytes on unencrypted connections. This can lead to resource exhaustion on the affected server, impacting availability.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, consider disabling unencrypted HTTP/2 support or applying network-level protections to limit connection attempts.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-xphw-4f88-5f39
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-56853"]
- Ecosystems
- []
- Database Specific Severity
- HIGH
- Cvss Version
- 3.1
Threat ID: 6a7ff608bf8831d5398816af
Added to database: 08/15/2026, 05:15:52 UTC
Last enriched: 08/15/2026, 05:26:05 UTC
Last updated: 08/15/2026, 05:41:00 UTC
Views: 4
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