Ignore unrelated, unauthenticated hashes in Lookup in golang.org/x/mod/sumdb (CVE-2026-56864) | HOL Guard CVE

High · CVSS 7.5CVE-2026-56864

Ignore unrelated, unauthenticated hashes in Lookup in golang.org/x/mod/sumdb

Answer in brief

CVE-2026-56864 records a High severity (CVSS 7.5) vulnerability in Ignore unrelated, unauthenticated hashes in Lookup in golang.org/x/mod/sumdb. The current sources do not mark it as known exploited. The current feed maps Go toolchain/cmd/go (generic), golang.org/x/mod/golang.org/x/mod/sumdb (generic), golang.org/x/mod (go), toolchain (go). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

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

Published Aug 13, 2026Updated Sep 3, 2026Source checked Sep 28, 2026First seen by HOL Aug 13, 2026Material review Sep 3, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.5
Exploitation: Not marked as known exploited
Affected software: 4 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.5. 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 Go toolchain/cmd/go (generic), golang.org/x/mod/golang.org/x/mod/sumdb (generic), golang.org/x/mod (go), toolchain (go). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Go toolchain/cmd/gogeneric	>=0 <1.25.13 \|\| >=1.26.0-0 <1.26.6 \|\| >=1.27.0-0 <1.27.0-rc.3	1.25.13, 1.26.6, 1.27.0-rc.3
golang.org/x/mod/golang.org/x/mod/sumdbgeneric	>=0 <0.40.0	0.40.0
golang.org/x/modgo	>=0 <0.40.0	0.40.0
toolchaingo	>=0 <1.25.13 >=1.26.0-0 <1.26.6 >=1.27.0-0 <1.27.0-rc.3	1.25.13, 1.26.6, 1.27.0-rc.3

Recommended response

Check inventory. Check lockfiles and deployed manifests for Go toolchain/cmd/go, golang.org/x/mod/golang.org/x/mod/sumdb, golang.org/x/mod.
Review the reported fix. Update Go toolchain/cmd/go to 1.25.13; golang.org/x/mod/golang.org/x/mod/sumdb to 0.40.0; golang.org/x/mod to 0.40.0; toolchain to 1.25.13 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 13, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 3, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 13, 2026

Sources and claim methodology

Upstream source description

A malicious GOSUMDB was capable of serving arbitrary module content not contained within the transparency log. This attack allows for a coordinating GOPROXY and GOSUMDB to serve a client malicious module content that cannot be detected by evaluating the transparency log. In order to determine if you have been affected: rm -r go.sum go.work.sum vendor/ && go mod tidy

Quoted source text, attributed separately from HOL analysis.