GO-2026-6603

    Dashboard / Vulnerabilities / GO-2026-6603

    GO-2026-6603

    Published: 8 Oct 2026Last Modified: 8 Oct 2026

    Summary: HTTP/2 server memory exhaustion due to Trailer headers in net/http

    Details: When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead. For HTTP/2 servers, a malicious client can exploit this by sending a "Trailer" header that declares a large number of fields, causing the server to allocate a disproportionate amount of memory while bypassing Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits. This exploit is not applicable for HTTP/1 servers, which do not support multiplexing a large number of requests over one TCP connection, and whose Server.MaxHeaderBytes are calculated differently.

    References: https://go.dev/cl/847185, https://go.dev/cl/847314, https://go.dev/issue/81857, https://groups.google.com/g/golang-announce/c/U2fTuyDJznI, https://groups.google.com/g/golang-announce/c/ZPwCyRUuGBs

    Affected packages

    Package

    Name: stdlib

    Purl: pkg:golang/stdlib

    Affected ranges

    Type: SEMVER

    Events:

    Introduced- 0
    Fixed -1.26.9

    Affected versions

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High