CVE-2026-56865

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

Published Aug 13, 2026 CVSS 3.1 · 8.4 High EPSS < 1% KEV · Not listed
Description
A 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

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8935-1 Go vulnerabilities
History
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 8.4, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}

ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Golang
Golang mod
Gotoolchain
Gotoolchain cmd/go
Vendors & Products Golang
Golang mod
Gotoolchain
Gotoolchain cmd/go
Type Values Removed Values Added
Weaknesses CWE-347
Type Values Removed Values Added
Description A 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
Title Fix transparency log tile verification bypass in golang.org/x/mod/sumdb/tlog
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Go
Published
Updated
Aug 14, 2026, 3:34 PM
Reserved
Jun 23, 2026, 3:10 PM
Status
Awaiting Analysis
Published
Aug 13, 2026, 10:17 PM
Modified
Sep 3, 2026, 4:37 PM