--- title: "CVE-2026-42501\n | Ubuntu" description: Ubuntu is an open source software operating system that runs from the desktop, to the cloud, to all your internet connected things. url: https://ubuntu.com/security/CVE-2026-42501?format=md keywords: index, follow --- # CVE-2026-42501 Publication date 7 May 2026 Last updated 14 May 2026 --- Ubuntu priority **Medium** [Why this priority?](https://ubuntu.com/security/cves/about#priority ) ## Cvss 3 Severity Score **7.5 · High** [Score breakdown](https://ubuntu.com/security/CVE-2026-42501?format=md#impact-score) Toggle side navigation ## 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. [Read the notes from the security team](https://ubuntu.com/security/CVE-2026-42501?format=md#notes) ## Status Show unmaintained releases | Package | Ubuntu Release | Status | | --- | --- | --- | | golang-1.13 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Needs evaluation | | 20.04 LTS focal | Needs evaluation | | 18.04 LTS bionic | Needs evaluation | | 16.04 LTS xenial | Needs evaluation | | golang-1.18 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Needs evaluation | | 20.04 LTS focal | Needs evaluation | | 18.04 LTS bionic | Needs evaluation | | 16.04 LTS xenial | Needs evaluation | | golang-1.23 | 26.04 LTS resolute | Needs evaluation | | 25.10 questing | Ignored end of life, was needs-triage | | 24.04 LTS noble | Needs evaluation | | 22.04 LTS jammy | Needs evaluation | | golang-1.24 | 26.04 LTS resolute | Needs evaluation | | 25.10 questing | Ignored end of life, was needs-triage | | 24.04 LTS noble | Needs evaluation | | 22.04 LTS jammy | Needs evaluation | | golang-1.25 | 26.04 LTS resolute | Needs evaluation | | 25.10 questing | Ignored end of life, was needs-triage | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Not in release | | golang | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Not in release | | golang-1.10 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Not in release | | 18.04 LTS bionic | Needs evaluation | | 16.04 LTS xenial | Needs evaluation | | 14.04 LTS trusty | Needs evaluation | | golang-1.14 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Not in release | | 20.04 LTS focal | Needs evaluation | | golang-1.16 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Not in release | | 20.04 LTS focal | Needs evaluation | | 18.04 LTS bionic | Needs evaluation | | golang-1.17 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Needs evaluation | | golang-1.20 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Needs evaluation | | 20.04 LTS focal | Needs evaluation | | golang-1.21 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Needs evaluation | | 22.04 LTS jammy | Needs evaluation | | 20.04 LTS focal | Needs evaluation | | golang-1.22 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Needs evaluation | | 22.04 LTS jammy | Needs evaluation | | 20.04 LTS focal | Needs evaluation | | golang-1.6 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Not in release | | 16.04 LTS xenial | Needs evaluation | | golang-1.8 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Not in release | | 18.04 LTS bionic | Needs evaluation | | golang-1.9 | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 24.04 LTS noble | Not in release | | 22.04 LTS jammy | Not in release | | 18.04 LTS bionic | Needs evaluation | --- * [How can I get the fixes?](https://ubuntu.com/security/cves/about#security) * [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses) ## Notes --- ### [mdeslaur](https://launchpad.net/~mdeslaur) Packages built using golang need to be rebuilt once the vulnerability has been fixed. This CVE entry does not list packages that need rebuilding outside of the main repository or the Ubuntu variants with PPA overlays. Warning: do not include nullboot in the list of no-change rebuilds after fixing an issue in golang. ## Severity score breakdown CVSS version: CVSS v3.0 **Base score** 7.5 · High * Base metrics | Parameter | Value | | --- | --- | | Attack vector | Network | | Attack complexity | High | | Privileges required | None | | User interaction | Required | | Scope | Unchanged | | Confidentiality impact | High | | Integrity impact | High | | Availability impact | High | * Scores | Parameter | Value | | --- | --- | | Base score | 7.5 · High | | Exploitability score | - | | Impact score | - | **Vector:** CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H ## References * [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-42501) * [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-42501) * [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-42501) * [Debian](https://security-tracker.debian.org/tracker/CVE-2026-42501) ### Other references * * * * * * *