CVE-2026-56865Fix transparency log tile verification bypass in golang.org/x/mod/sumdb/tlog
Updated under an hour ago ()
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It affects Go toolchain cmd/go and 1 other product. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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
- CVSS
- 8.4 HIGH (v3.1, CISA ADP)CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- CWE-347
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Go
- NVD analysis
- Awaiting Analysis
- Record last updated
- Aug 14, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Go toolchain cmd/go go_toolchain:cmd_go (from the name) | before 1.25.13; from 1.26.0-0 before 1.26.6; 1.27.0-0 builds before 1.27.0-rc.3 | CNA record |
golang.org/x/mod golang.org/x/mod/sumdb/tlog golang.org_x_mod:sumdb_tlog (from the name) | before 0.40.0 | CNA record |
References
- https://go.dev/issue/80744
- https://groups.google.com/g/golang-announce/c/94pEornpRlI
- https://go.dev/cl/814960
- https://go.dev/cl/815020
- https://pkg.go.dev/vuln/GO-2026-6179
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.