Unknown severity · Source severity not reportedCVE-2026-78659

HTTP/2 server memory exhaustion due to Trailer headers in net/httpCVE-2026-78659

Answer in brief

CVE-2026-78659 records a Unknown severity vulnerability in HTTP/2 server memory exhaustion due to Trailer headers in net/http. The current sources do not mark it as known exploited. The current feed maps golang.org/x/net/golang.org/x/net/http2 (generic), Go standard library/net/http (generic), Go standard library/net/http/internal/http2 (generic), golang.org/x/net (go) and additional mapped packages. Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 8, 2026Updated Oct 8, 2026Source checked Oct 9, 2026First seen by HOL Oct 8, 2026Material review Oct 8, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 6 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps golang.org/x/net/golang.org/x/net/http2 (generic), Go standard library/net/http (generic), Go standard library/net/http/internal/http2 (generic), golang.org/x/net (go) and additional mapped packages. Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
golang.org/x/net/golang.org/x/net/http2generic	>=0 <0.60.0	0.60.0
Go standard library/net/httpgeneric	>=0 <1.26.9	1.26.9
Go standard library/net/http/internal/http2generic	>=1.27.0-0 <1.27.2	1.27.2
golang.org/x/netgo	>=0 <0.60.0	0.60.0
stdlibgo	>=0 <1.26.9	1.26.9
stdlibgo	>=1.27.0-0 <1.27.2	1.27.2

Recommended response

Check inventory. Check lockfiles and deployed manifests for golang.org/x/net/golang.org/x/net/http2, Go standard library/net/http, Go standard library/net/http/internal/http2.
Review the reported fix. Update golang.org/x/net/golang.org/x/net/http2 to 0.60.0; Go standard library/net/http to 1.26.9; Go standard library/net/http/internal/http2 to 1.27.2; golang.org/x/net to 0.60.0; stdlib to 1.26.9; stdlib to 1.27.2 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 8, 2026

Sources and claim methodology

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.