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CVE-2026-56865— Fix transparency log tile verification bypass in golang.org/x/mod/sumdb/tlog

Quick assessment

Affected
Go toolchain cmd/go
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Google Go是美国Google公司开源的一款支持并发编程的脚本语言。 Google Go 1.25.13之前版本、1.26.0-0至1.26.6之前版本和1.27.0-0至1.27.0-rc.3之前版本，以及golang.org/x/mod/sumdb/tlog 0.40.0之前版本存在加密问题漏洞，该漏洞源于恶意GOPROXY伪造最多两个sumdb tiles，导致请求的模块绕过GOSUMDB检查并将攻击者控制的模块内容持久化到本地Go模块缓存，可能提供无法通过透明日志检测的恶意模块内容。

AI Predicted 7.5 Difficulty: Moderate EPSS 0.13% · P2

Affected Version Matrix 4

VendorProduct Version RangeStatus
Go toolchain cmd/go < 1.25.13 affected
1.26.0-0< 1.26.6 affected
1.27.0-0< 1.27.0-rc.3 affected
golang.org/x/mod golang.org/x/mod/sumdb/tlog < 0.40.0 affected
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I. Basic Information for CVE-2026-56865

Vulnerability Information
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Vulnerability Title
Fix transparency log tile verification bypass in golang.org/x/mod/sumdb/tlog
Source: CVE Program / CVE List V5
Vulnerability 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
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Google Go 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Google Go是美国Google公司开源的一款支持并发编程的脚本语言。 Google Go 1.25.13之前版本、1.26.0-0至1.26.6之前版本和1.27.0-0至1.27.0-rc.3之前版本，以及golang.org/x/mod/sumdb/tlog 0.40.0之前版本存在加密问题漏洞，该漏洞源于恶意GOPROXY伪造最多两个sumdb tiles，导致请求的模块绕过GOSUMDB检查并将攻击者控制的模块内容持久化到本地Go模块缓存，可能提供无法通过透明日志检测的恶意模块内容。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Go toolchain cmd/go 0 ~ 1.25.13 -
golang.org/x/mod golang.org/x/mod/sumdb/tlog 0 ~ 0.40.0 -

II. Public POCs for CVE-2026-56865

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III. Intelligence Information for CVE-2026-56865

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Patches & Fixes for CVE-2026-56865 (2)

Vendor Advisories for CVE-2026-56865 (2)

News Coverage for CVE-2026-56865 (1)

IV. Related Vulnerabilities

Same product: cmd/go
Same vendor: Go toolchain

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