# CVE-2026-42501: Malicious module proxy can bypass checksum database in cmd/go CVE-2026-42501 is fixed in 15 products on 2 platforms, first by Go Programming Language 1.26.3, released May 7, 2026. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2026-42501 - Priority: High - CVSS: 7.5 (Important) - EPSS: 0.0023 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: May 7, 2026 - Weakness: CWE-347: Improper Verification of Cryptographic Signature - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42501 ## Description 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. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Windows apps | Go Programming Language | 1.26.3 | [Go Programming Language 1.26.3](https://patchblox.com/security/data/fix/windows-app/golang.go-1.26.3.md) | May 7, 2026 | | Linux | delve RHEL 8 | 0:1.25.2-1.module+el8.10.0+23746+9db33b5e | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | delve almalinux 8 | 1.25.2-1.module_el8.10.0+4074+24330916 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | delve ol 8 | 0:1.25.2-1.0.1.module+el8.10.0+90715+2d4d8dfd | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | delve rocky 8 | 0:1.25.2-1.module+el8.10.0+40035+ee0a7047 | [RLSA-2026:22112](https://patchblox.com/security/data/fix/linux/rlsa-2026-22112.md) | Aug 26, 2026 | | Linux | go-toolset RHEL 8 | 0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | go-toolset RHEL 9 | 0:1.26.3-1.el9_8 | [RHSA-2026:22121](https://patchblox.com/security/data/fix/linux/rhsa-2026-22121.md) | Jun 1, 2026 | | Linux | go-toolset almalinux 8 | 1.25.10-1.module_el8.10.0+4187+c45165c4 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | go-toolset almalinux 9 | 1.26.3-1.el9_8 | [ALSA-2026:22121](https://patchblox.com/security/data/fix/linux/alsa-2026-22121.md) | Jun 1, 2026 | | Linux | go-toolset ol 10 | 0:1.26.5-1.0.1.el10_2 | [ELSA-2026-22120](https://patchblox.com/security/data/fix/linux/elsa-2026-22120.md) | Jul 21, 2026 | | Linux | go-toolset ol 8 | 0:1.25.9-1.0.1.module+el8.10.0+90898+1e3c34bb | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | go-toolset ol 9 | 0:1.26.3-1.0.1.el9_8 | [ELSA-2026-22121](https://patchblox.com/security/data/fix/linux/elsa-2026-22121.md) | Jun 23, 2026 | | Linux | go1.25-openssl opensuse-leap 16.0 | 1.25.12-160000.1.1 | [OPENSUSE-SU-2026:21319-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21319-1.md) | Jul 13, 2026 | | Linux | go1.25-openssl sles 16.0 | 1.25.12-160000.1.1 | [SUSE-SU-2026:22638-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22638-1.md) | Jul 13, 2026 | | Linux | go1.26-openssl opensuse-leap 16.0 | 1.26.4-160000.1.1 | [OPENSUSE-SU-2026:21254-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21254-1.md) | Jul 7, 2026 | | Linux | go1.26-openssl sles 16.0 | 1.26.4-160000.1.1 | [SUSE-SU-2026:22572-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22572-1.md) | Jul 7, 2026 | | Linux | golang RHEL 10 | 1.26.5-1.el10_0 | [RHSA-2026:49702](https://patchblox.com/security/data/fix/linux/rhsa-2026-49702.md) | May 27, 2026 | | Linux | golang RHEL 8 | 0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang RHEL 9 | 0:1.26.3-1.el9_8 | [RHSA-2026:22121](https://patchblox.com/security/data/fix/linux/rhsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang almalinux 8 | 1.25.10-1.module_el8.10.0+4187+c45165c4 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang almalinux 9 | 1.26.3-1.el9_8 | [ALSA-2026:22121](https://patchblox.com/security/data/fix/linux/alsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang amzn 2023 | 1.25.10-1.amzn2023.0.1 | [ALAS2023-2026-1743](https://patchblox.com/security/data/fix/linux/alas2023-2026-1743.md) | May 25, 2026 | | Linux | golang ol 10 | 0:1.26.5-1.0.1.el10_2 | [ELSA-2026-22120](https://patchblox.com/security/data/fix/linux/elsa-2026-22120.md) | Jul 21, 2026 | | Linux | golang ol 8 | 0:1.25.9-1.0.1.module+el8.10.0+90898+1e3c34bb | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | golang ol 9 | 0:1.26.3-1.0.1.el9_8 | [ELSA-2026-22121](https://patchblox.com/security/data/fix/linux/elsa-2026-22121.md) | Jun 23, 2026 | | Linux | golang rocky 10 | 0:1.26.3-4.el10_2 | [RLSA-2026:22120](https://patchblox.com/security/data/fix/linux/rlsa-2026-22120.md) | Aug 26, 2026 | | Linux | golang rocky 8 | 0:1.25.10-1.module+el8.10.0+40200+0fd0f175 | [RLSA-2026:22112](https://patchblox.com/security/data/fix/linux/rlsa-2026-22112.md) | Aug 26, 2026 | | Linux | golang rocky 9 | 0:1.26.3-1.el9_8 | [RLSA-2026:22121](https://patchblox.com/security/data/fix/linux/rlsa-2026-22121.md) | Aug 26, 2026 | | Linux | golang-1.26 Debian 14 | 1.26.3-1 | [DEBIAN-CVE-2026-42501](https://patchblox.com/security/data/fix/linux/debian-cve-2026-42501.md) | May 27, 2026 | | Linux | golang-bin RHEL 8 | 0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-bin RHEL 9 | 0:1.26.3-1.el9_8 | [RHSA-2026:22121](https://patchblox.com/security/data/fix/linux/rhsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-bin almalinux 8 | 1.25.10-1.module_el8.10.0+4187+c45165c4 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-bin almalinux 9 | 1.26.3-1.el9_8 | [ALSA-2026:22121](https://patchblox.com/security/data/fix/linux/alsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-bin amzn 2023 | 1.25.10-1.amzn2023.0.1 | [ALAS2023-2026-1743](https://patchblox.com/security/data/fix/linux/alas2023-2026-1743.md) | May 25, 2026 | | Linux | golang-bin ol 10 | 0:1.26.5-1.0.1.el10_2 | [ELSA-2026-22120](https://patchblox.com/security/data/fix/linux/elsa-2026-22120.md) | Jul 21, 2026 | | Linux | golang-bin ol 8 | 0:1.25.9-1.0.1.module+el8.10.0+90898+1e3c34bb | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | golang-bin ol 9 | 0:1.26.3-1.0.1.el9_8 | [ELSA-2026-22121](https://patchblox.com/security/data/fix/linux/elsa-2026-22121.md) | Jun 23, 2026 | | Linux | golang-docs RHEL 8 | 0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-docs RHEL 9 | 0:1.26.3-1.el9_8 | [RHSA-2026:22121](https://patchblox.com/security/data/fix/linux/rhsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-docs almalinux 8 | 1.25.10-1.module_el8.10.0+4187+c45165c4 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-docs almalinux 9 | 1.26.3-1.el9_8 | [ALSA-2026:22121](https://patchblox.com/security/data/fix/linux/alsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-docs amzn 2023 | 1.25.10-1.amzn2023.0.1 | [ALAS2023-2026-1743](https://patchblox.com/security/data/fix/linux/alas2023-2026-1743.md) | May 25, 2026 | | Linux | golang-docs ol 10 | 0:1.26.5-1.0.1.el10_2 | [ELSA-2026-22120](https://patchblox.com/security/data/fix/linux/elsa-2026-22120.md) | Jul 21, 2026 | | Linux | golang-docs ol 8 | 0:1.25.9-1.0.1.module+el8.10.0+90898+1e3c34bb | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | golang-docs ol 9 | 0:1.26.3-1.0.1.el9_8 | [ELSA-2026-22121](https://patchblox.com/security/data/fix/linux/elsa-2026-22121.md) | Jun 23, 2026 | | Linux | golang-misc RHEL 8 | 0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-misc RHEL 9 | 0:1.26.3-1.el9_8 | [RHSA-2026:22121](https://patchblox.com/security/data/fix/linux/rhsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-misc almalinux 8 | 1.25.10-1.module_el8.10.0+4187+c45165c4 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-misc almalinux 9 | 1.26.3-1.el9_8 | [ALSA-2026:22121](https://patchblox.com/security/data/fix/linux/alsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-misc amzn 2023 | 1.25.10-1.amzn2023.0.1 | [ALAS2023-2026-1743](https://patchblox.com/security/data/fix/linux/alas2023-2026-1743.md) | May 25, 2026 | | Linux | golang-misc ol 10 | 0:1.26.5-1.0.1.el10_2 | [ELSA-2026-22120](https://patchblox.com/security/data/fix/linux/elsa-2026-22120.md) | Jul 21, 2026 | | Linux | golang-misc ol 8 | 0:1.25.9-1.0.1.module+el8.10.0+90898+1e3c34bb | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | golang-misc ol 9 | 0:1.26.3-1.0.1.el9_8 | [ELSA-2026-22121](https://patchblox.com/security/data/fix/linux/elsa-2026-22121.md) | Jun 23, 2026 | | Linux | golang-race RHEL 8 | 0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-race RHEL 9 | 0:1.26.3-1.el9_8 | [RHSA-2026:22121](https://patchblox.com/security/data/fix/linux/rhsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-race almalinux 8 | 1.25.10-1.module_el8.10.0+4187+c45165c4 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-race almalinux 9 | 1.26.3-1.el9_8 | [ALSA-2026:22121](https://patchblox.com/security/data/fix/linux/alsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-race ol 10 | 0:1.26.5-1.0.1.el10_2 | [ELSA-2026-22120](https://patchblox.com/security/data/fix/linux/elsa-2026-22120.md) | Jul 21, 2026 | | Linux | golang-race ol 8 | 0:1.25.9-1.0.1.module+el8.10.0+90898+1e3c34bb | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | golang-race ol 9 | 0:1.26.3-1.0.1.el9_8 | [ELSA-2026-22121](https://patchblox.com/security/data/fix/linux/elsa-2026-22121.md) | Jun 23, 2026 | | Linux | golang-shared amzn 2023 | 1.25.10-1.amzn2023.0.1 | [ALAS2023-2026-1743](https://patchblox.com/security/data/fix/linux/alas2023-2026-1743.md) | May 25, 2026 | | Linux | golang-src RHEL 8 | 0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-src RHEL 9 | 0:1.26.3-1.el9_8 | [RHSA-2026:22121](https://patchblox.com/security/data/fix/linux/rhsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-src almalinux 8 | 1.25.10-1.module_el8.10.0+4187+c45165c4 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-src almalinux 9 | 1.26.3-1.el9_8 | [ALSA-2026:22121](https://patchblox.com/security/data/fix/linux/alsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-src amzn 2023 | 1.25.10-1.amzn2023.0.1 | [ALAS2023-2026-1743](https://patchblox.com/security/data/fix/linux/alas2023-2026-1743.md) | May 25, 2026 | | Linux | golang-src ol 10 | 0:1.26.5-1.0.1.el10_2 | [ELSA-2026-22120](https://patchblox.com/security/data/fix/linux/elsa-2026-22120.md) | Jul 21, 2026 | | Linux | golang-src ol 8 | 0:1.25.9-1.0.1.module+el8.10.0+90898+1e3c34bb | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | golang-src ol 9 | 0:1.26.3-1.0.1.el9_8 | [ELSA-2026-22121](https://patchblox.com/security/data/fix/linux/elsa-2026-22121.md) | Jun 23, 2026 | | Linux | golang-tests RHEL 8 | 0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 | [RHSA-2026:22112](https://patchblox.com/security/data/fix/linux/rhsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-tests RHEL 9 | 0:1.26.3-1.el9_8 | [RHSA-2026:22121](https://patchblox.com/security/data/fix/linux/rhsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-tests almalinux 8 | 1.25.10-1.module_el8.10.0+4187+c45165c4 | [ALSA-2026:22112](https://patchblox.com/security/data/fix/linux/alsa-2026-22112.md) | Jun 1, 2026 | | Linux | golang-tests almalinux 9 | 1.26.3-1.el9_8 | [ALSA-2026:22121](https://patchblox.com/security/data/fix/linux/alsa-2026-22121.md) | Jun 1, 2026 | | Linux | golang-tests amzn 2023 | 1.25.10-1.amzn2023.0.1 | [ALAS2023-2026-1743](https://patchblox.com/security/data/fix/linux/alas2023-2026-1743.md) | May 25, 2026 | | Linux | golang-tests ol 10 | 0:1.26.5-1.0.1.el10_2 | [ELSA-2026-22120](https://patchblox.com/security/data/fix/linux/elsa-2026-22120.md) | Jul 21, 2026 | | Linux | golang-tests ol 8 | 0:1.25.9-1.0.1.module+el8.10.0+90898+1e3c34bb | [ELSA-2026-22112](https://patchblox.com/security/data/fix/linux/elsa-2026-22112.md) | Jun 2, 2026 | | Linux | golang-tests ol 9 | 0:1.26.3-1.0.1.el9_8 | [ELSA-2026-22121](https://patchblox.com/security/data/fix/linux/elsa-2026-22121.md) | Jun 23, 2026 | | Linux | govulncheck-vulndb opensuse-leap 16.0 | 0.0.20260723T184607-160000.1.1 | [OPENSUSE-SU-2026:21483-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21483-1.md) | Jul 30, 2026 | --- Data as of 2026-11-08T06:59:42Z UTC. 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