Fix transparency log tile verification bypass in golang.org/x/mod/sumdb/tlog

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-56865
StatePUBLISHED
AssignerGo
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-13 22:17:22 UTC
Updated2026-08-14 16:16:57 UTC
DescriptionA malicious GOPROXY was previously capable of forging up to two sumdb tiles that allow for a requested module to bypass the GOSUMDB check and persist attacker-controlled module content to a local Go module cache. This attack allows for a malicious GOPROXY to serve malicious module content that cannot be detected by evaluating the transparency log. All tiles are now correctly verified against their parents. In order to determine if you have been affected: rm -r go.sum go.work.sum vendor/ && go mod tidy

Risk And Classification

Primary CVSS: v3.1 8.4 HIGH from ADP

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Problem Types: CWE-347 | CWE-347: Improper Verification of Cryptographic Signature | CWE-347 CWE-347 Improper Verification of Cryptographic Signature

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED8.4HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary8.4HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Go Toolchain Cmd/go affected 1.25.13 semver Not specified
CNA Go Toolchain Cmd/go affected 1.26.0-0 1.26.6 semver Not specified
CNA Go Toolchain Cmd/go affected 1.27.0-0 1.27.0-rc.3 semver Not specified
CNA Golang.orgxmod Golang.org/x/mod/sumdb/tlog affected 0.40.0 semver Not specified

References

ReferenceSourceLinkTags
go.dev/issue/80744 [email protected] go.dev
groups.google.com/g/golang-announce/c/94pEornpRlI [email protected] groups.google.com
go.dev/cl/814960 [email protected] go.dev
go.dev/cl/815020 [email protected] go.dev
pkg.go.dev/vuln/GO-2026-6179 [email protected] pkg.go.dev
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Filippo Valsorda (Geomys) (en)

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