CVE-2026-56864: A malicious GOSUMDB was capable of serving arbitrary module content not contained within the transparency log. This attack allows for a coordinating GOPROXY…

PriorityP346high7.5CVSS 3.1

AVNACLPRNUINSUCHINAN

EPSS

0.30%

22.1th percentile

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

Affected

4 ranges

Vendor	Product	Version range	Fixed in
go_toolchain	cmd_go	< 1.25.13	1.25.13
go_toolchain	cmd_go	>= 1.26.0-0 < 1.26.6	1.26.6
go_toolchain	cmd_go	>= 1.27.0-0 < 1.27.0-rc.3	1.27.0-rc.3
golang.org	x_mod_golang.org_x_mod_sumdb	< 0.40.0	0.40.0

Stop checking back — get the weekly exploitation signal.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.