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Fencer Vulns
high 7.5

CVE-2026-42501 json

Malicious module proxy can bypass checksum database in cmd/go

published 2026-05-07 6 mo ago modified 2026-09-08 2 mo ago also BIT-golang-2026-42501 , EUVD-2026-28433 , GO-2026-4984

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

Summary

A malicious module proxy can exploit a flaw in the go command's validation of module checksums to bypass checksum database validation. This vulnerability affects any user using an untrusted module proxy (GOMODPROXY) or checksum database (GOSUMDB). A malicious module proxy can serve altered versions of the Go toolchain. When selecting a different version of the Go toolchain than the currently installed toolchain (due to the GOTOOLCHAIN environment variable, or a go.work or go.mod with a toolchain line), the go command will download and execute a toolchain provided by the module proxy. A malicious module proxy can bypass checksum database validation for this downloaded toolchain. Since this vulnerability affects the security of toolchain downloads, setting GOTOOLCHAIN to a fixed version is not sufficient. You must upgrade your base Go toolchain. The go tool always validates the hash of a toolchain before executing it, so fixed versions will refuse to execute any cached, altered versions of the toolchain. The go tool trusts go.sum files to contain accurate hashes of the current module's dependencies. A malicious proxy exploiting this vulnerability to serve an altered module will have caused an incorrect hash to be recorded in the go.sum. Users who have configured a non-trusted GOPROXY can determine if they have been affected by running "rm go.sum ; go mod tidy ; go mod verify", which will revalidate all dependencies of the current module. The specific flaw in more detail: The go command consults the checksum database to validate downloaded modules, when a module is not listed in the go.sum file. It verifies that the module hash reported by the checksum database matches the hash of the downloaded module. If, however, the checksum database returns a successful response that contains no entry for the module, the go command incorrectly permitted validation to succeed. A module proxy may mirror or proxy the checksum database, in which case the go command will not connect to the checksum database directly. Checksums reported by the checksum database are cryptographically signed, so a malicious proxy cannot alter the reported checksum for a module. However, a proxy which returns an empty checksum response, or a checksum response for an unrelated module, could cause the go command to proceed as if a downloaded module has been validated.

Patch / fix

  • bitnami golang 1.25.10, 1.26.3
  • go toolchain 1.25.10, 1.26.3
  • Go toolchain cmd/go 1.25.10, 1.26.3
  • golang-1.26 Debian 14 1.26.3-1

debian advisories DEBIAN-CVE-2026-42501

  • golang-fips1.25 hummingbird 1 1.25.9-0.1.1.hum1
  • golang-fips1.25-bin hummingbird 1 1.25.9-0.1.1.hum1
  • golang-fips1.25-src hummingbird 1 1.25.9-0.1.1.hum1
  • golang-fips1.25-misc hummingbird 1 1.25.9-0.1.1.hum1
  • golang-fips1.25-race hummingbird 1 1.25.9-0.1.1.hum1
  • golang-fips1.25-tests hummingbird 1 1.25.9-0.1.1.hum1
  • golang RHEL 9 1.26.3-1.el9_8
  • go-toolset RHEL 9 1.26.3-1.el9_8

red hat advisories RHSA-2026:61253RHSA-2026:57649RHSA-2026:49712RHSA-2026:49702RHSA-2026:32987RHSA-2026:22121

  • go1.25-openssl SLES for SAP applications 16.0, SLES 16.0 1.25.12-160000.1.1
  • go1.26-openssl SLES for SAP applications 16.0, SLES 16.0 1.26.4-160000.1.1

suse advisories SUSE-SU-2026:22638-1SUSE-SU-2026:22572-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1
  • go1.25-openssl openSUSE Leap 16.0 1.25.12-160000.1.1
  • go1.26-openssl openSUSE Leap 16.0 1.26.4-160000.1.1
  • opa openSUSE Tumbleweed 1.16.2-1.1
  • go1.26 openSUSE Tumbleweed 1.26.3-1.1
  • go1.25 openSUSE Tumbleweed 1.25.10-1.1

opensuse advisories openSUSE-SU-2026:21483-1openSUSE-SU-2026:21319-1openSUSE-SU-2026:21254-1openSUSE-SU-2026:10755-1openSUSE-SU-2026:10741-1openSUSE-SU-2026:10723-1

  • delve AlmaLinux 8 1.25.2-1.module_el8.10.0+4074+24330916
  • golang AlmaLinux 8 1.25.10-1.module_el8.10.0+4187+c45165c4
  • go-toolset AlmaLinux 8 1.25.10-1.module_el8.10.0+4187+c45165c4
  • golang-bin AlmaLinux 8 1.25.10-1.module_el8.10.0+4187+c45165c4
  • golang-src AlmaLinux 8 1.25.10-1.module_el8.10.0+4187+c45165c4
  • golang-misc AlmaLinux 8 1.25.10-1.module_el8.10.0+4187+c45165c4
  • golang-race AlmaLinux 8 1.25.10-1.module_el8.10.0+4187+c45165c4
  • golang-tests AlmaLinux 8 1.25.10-1.module_el8.10.0+4187+c45165c4

almalinux advisories ALSA-2026:22112ALSA-2026:22121

  • golang Rocky Linux 10 1.26.3-4.el10_2
  • golang Rocky Linux 9 1.26.3-1.el9_8
  • delve Rocky Linux 8 1.25.2-1.module+el8.10.0+40035+ee0a7047
  • golang Rocky Linux 8 1.25.10-1.module+el8.10.0+40200+0fd0f175

rocky linux advisories RLSA-2026:22120RLSA-2026:22121RLSA-2026:22112

  • go Alpine 3.23 1.25.10-r0
  • go Alpine 3.24 1.26.3-r0
  • rclone Alpine 3.24 1.74.1-r0

alpine advisories ALPINE-CVE-2026-42501

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-42501 updated cvss 5.3

cmd/go: golang: Go command (cmd/go): Integrity bypass due to checksum validation flaw via malicious module proxy

  • Red Hat Exploit Intelligence exploit-intelligence-tech-preview/vulnerability-analysis-rhel9 Red Hat Multicluster Engine for Kubernetes multicluster-engine/work-rhel9, multicluster-engine/maestro-rhel9, multicluster-engine/placement-rhel9, multicluster-engine/registration-rhel9, multicluster-engine/addon-manager-rhel9, multicluster-engine/multicloud-manager-rhel9, +4 more Red Hat OpenShift API for Data Protection oadp/oadp-velero-rhel9, multicluster-engine/work-rhel9, openshift4/ose-hypershift-rhel9, multicluster-engine/maestro-rhel9, multicluster-engine/placement-rhel9, rhacm2/config-policy-controller-rhel9, +11 more Red Hat OpenShift Service Mesh 2 rh-osbs/openshift-golang-builder Red Hat OpenShift Service Mesh 3 rh-osbs/openshift-golang-builder
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/klusterlet-addon-controller-rhel9
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AI (RHEL AI) 3 golang Red Hat OpenShift Container Platform 4 openshift4/ose-hypershift-rhel9, rh-osbs/openshift-golang-builder Red Hat OpenShift Container Platform 5 rh-osbs/openshift-golang-builder Red Hat OpenShift Virtualization 4 rh-osbs/openshift-golang-builder
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux AppStream (v. 8) delve 1.25.2-1.module+el8.10.0+23746+9db33b5e, golang 1.25.10-1.module+el8.10.0+24308+5c4a16b7, go-toolset 1.25.10-1.module+el8.10.0+24308+5c4a16b7, golang-bin 1.25.10-1.module+el8.10.0+24308+5c4a16b7, golang-src 1.25.10-1.module+el8.10.0+24308+5c4a16b7, golang-misc 1.25.10-1.module+el8.10.0+24308+5c4a16b7, +2 more
    fixed: vendor fix RHSA-2026:22112
  • Red Hat Enterprise Linux AppStream (v. 9) golang 1.26.3-1.el9_8, go-toolset 1.26.3-1.el9_8, golang-bin 1.26.3-1.el9_8, golang-src 1.26.3-1.el9_8, golang-misc 1.26.3-1.el9_8, golang-race 1.26.3-1.el9_8, +1 more
    fixed: vendor fix RHSA-2026:22121
  • Red Hat Enterprise Linux AppStream (v. 10) golang 1.26.3-4.el10_2, go-toolset 1.26.3-4.el10_2, golang-bin 1.26.3-4.el10_2, golang-src 1.26.3-4.el10_2, golang-misc 1.26.3-4.el10_2, golang-race 1.26.3-4.el10_2, +1 more
    fixed: vendor fix RHSA-2026:22120
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) golang 1.26.5-1.el9_2, go-toolset 1.26.5-1.el9_2, golang-bin 1.26.5-1.el9_2, golang-src 1.26.5-1.el9_2, golang-misc 1.26.5-1.el9_2, golang-race 1.26.5-1.el9_2, +1 more
    fixed: vendor fix RHSA-2026:61253
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) golang 1.26.5-1.el9_4, go-toolset 1.26.5-1.el9_4, golang-bin 1.26.5-1.el9_4, golang-src 1.26.5-1.el9_4, golang-misc 1.26.5-1.el9_4, golang-race 1.26.5-1.el9_4, +1 more
    fixed: vendor fix RHSA-2026:57649
show 5 more
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) golang 1.26.5-1.el10_0, go-toolset 1.26.5-1.el10_0, golang-bin 1.26.5-1.el10_0, golang-src 1.26.5-1.el10_0, golang-misc 1.26.5-1.el10_0, golang-race 1.26.5-1.el10_0, +1 more
    fixed: vendor fix RHSA-2026:49702
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) golang 1.26.5-1.el9_6, go-toolset 1.26.5-1.el9_6, golang-bin 1.26.5-1.el9_6, golang-src 1.26.5-1.el9_6, golang-misc 1.26.5-1.el9_6, golang-race 1.26.5-1.el9_6, +1 more
    fixed: vendor fix RHSA-2026:49712
  • Red Hat Hardened Images golang1.26 1.26.4-2.hum1, golang1.25 1.25.11-2.hum1, golang1.26-bin 1.26.4-2.hum1, golang1.26-src 1.26.4-2.hum1, golang1.25-bin 1.25.11-2.hum1, golang1.25-src 1.25.11-2.hum1, +10 more
    fixed: vendor fix RHSA-2026:32987
  • Red Hat Multicluster Engine for Kubernetes multicluster-engine/backplane-rhel9-operator
    not affected: vulnerable code not present
  • Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/config-policy-controller-rhel9, rhacm2/governance-policy-propagator-rhel9, rhacm2/acm-governance-policy-framework-addon-rhel9, rhacm2/acm-governance-policy-addon-controller-rhel9
    not affected: vulnerable code not in execute path

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
6 mo ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
bitnami golang
<1.25.10
>=1.26.0-0, <1.26.3
1.25.10
1.26.3
go toolchain
<1.25.10
>=1.26.0-0, <1.26.3
1.25.10
1.26.3

Affected products

  • Go toolchain cmd/go

Classification

Weakness
  • CWE-347 Improper Verification of Cryptographic Signature

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.