NVD / CVE Program· CNA Go

CVE-2026-42501: Malicious module proxy can bypass checksum database in cmd/go

Noroxi assessment

Priority: Monitor (action score 30/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.23% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. Special conditions such as timing or configuration are required.
Fixed version: Go toolchain cmd/go 1.25.10, 1.26.3.

Low priority for now. Upgrade to Go toolchain cmd/go 1.25.10, 1.26.3 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

HighCVSS 7.5 · v3.1—No exploit Fix available

Published: May 7, 2026
Updated: Jun 17, 2026
EPSS: 0.2% · 13th percentile
CWE: CWE-347

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
golang	go	cpe:2.3:a:golang:go

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

golang gobefore 1.25.10
golang go1.26.0 and later · before 1.26.3

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Go). Independent of NVD's CPE analysis and usually ahead of it.

Go toolchain cmd/go
- before 1.25.10affected · semver
- 1.26.0-0 and later · before 1.26.3affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
AlmaLinux:8	delve	before 1.25.2-1.module_el8.10.0+4074+24330916	1.25.2-1.module_el8.10.0+4074+24330916
AlmaLinux:8	go-toolset	before 1.25.10-1.module_el8.10.0+4187+c45165c4	1.25.10-1.module_el8.10.0+4187+c45165c4
AlmaLinux:8	golang	before 1.25.10-1.module_el8.10.0+4187+c45165c4	1.25.10-1.module_el8.10.0+4187+c45165c4
AlmaLinux:8	golang-bin	before 1.25.10-1.module_el8.10.0+4187+c45165c4	1.25.10-1.module_el8.10.0+4187+c45165c4
AlmaLinux:8	golang-docs	before 1.25.10-1.module_el8.10.0+4187+c45165c4	1.25.10-1.module_el8.10.0+4187+c45165c4
AlmaLinux:8	golang-misc	before 1.25.10-1.module_el8.10.0+4187+c45165c4	1.25.10-1.module_el8.10.0+4187+c45165c4
AlmaLinux:8	golang-race	before 1.25.10-1.module_el8.10.0+4187+c45165c4	1.25.10-1.module_el8.10.0+4187+c45165c4
AlmaLinux:8	golang-src	before 1.25.10-1.module_el8.10.0+4187+c45165c4	1.25.10-1.module_el8.10.0+4187+c45165c4
AlmaLinux:8	golang-tests	before 1.25.10-1.module_el8.10.0+4187+c45165c4	1.25.10-1.module_el8.10.0+4187+c45165c4
AlmaLinux:9	go-toolset	before 1.26.3-1.el9_8	1.26.3-1.el9_8
AlmaLinux:9	golang	before 1.26.3-1.el9_8	1.26.3-1.el9_8
AlmaLinux:9	golang-bin	before 1.26.3-1.el9_8	1.26.3-1.el9_8
AlmaLinux:9	golang-docs	before 1.26.3-1.el9_8	1.26.3-1.el9_8
AlmaLinux:9	golang-misc	before 1.26.3-1.el9_8	1.26.3-1.el9_8
AlmaLinux:9	golang-race	before 1.26.3-1.el9_8	1.26.3-1.el9_8
AlmaLinux:9	golang-src	before 1.26.3-1.el9_8	1.26.3-1.el9_8
AlmaLinux:9	golang-tests	before 1.26.3-1.el9_8	1.26.3-1.el9_8
Debian:12	golang-1.19	from 0	—
Debian:13	golang-1.24	from 0	—
Debian:14	golang-1.26	before 1.26.3-1	1.26.3-1
Go	toolchain	from 1.26.0-0 · before 1.26.3	1.26.3
Go	toolchain	before 1.25.10	1.25.10
openSUSE:Tumbleweed	go1.25	before 1.25.10-1.1	1.25.10-1.1
openSUSE:Tumbleweed	go1.26	before 1.26.3-1.1	1.26.3-1.1

+83

Same product

golang: all records

Other highest-scoring records for the same primary product.

CVE-2018-7187The "go get" implementation in Go 1.9.4, when the -insecure command-line option is used, does not validate the import path (get/vcs.go only
54Plan
CVE-2018-16873In Go before 1.10.6 and 1.11.x before 1.11.3, the "go get" command is vulnerable to remote code execution when executed with the -u flag and
52Plan
CVE-2021-38297Go before 1.16.9 and 1.17.x before 1.17.2 has a Buffer Overflow via large arguments in a function invocation from a WASM module, when GOARCH
42Plan

Published before and after this one in the same product

← EarlierCVE-2026-39817May 7, 2026 · Invoking "go tool pack" does not sanitize output paths in cmd/go
23Monitor
← EarlierCVE-2026-39819May 7, 2026 · Invoking "go bug" follows symlinks in predictable temporary filenames in cmd/go
21Monitor
Later →CVE-2026-33811May 7, 2026 · Crash when handling long CNAME response in net
30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Go toolchain cmd/go	1.25.10	Vendor (CNA)
Go toolchain cmd/go	1.26.3	Vendor (CNA)
azl3 golang 1.27.0-1 on Azure Linux 3.0	—	Microsoft (MSRC)
almalinux:delve	1.25.2-1.module_el8.10.0+4074+24330916 · AlmaLinux:8	Package registry (OSV)
almalinux:go-toolset	1.25.10-1.module_el8.10.0+4187+c45165c4 · AlmaLinux:8	Package registry (OSV)
almalinux:golang	1.25.10-1.module_el8.10.0+4187+c45165c4 · AlmaLinux:8	Package registry (OSV)
almalinux:golang-bin	1.25.10-1.module_el8.10.0+4187+c45165c4 · AlmaLinux:8	Package registry (OSV)
almalinux:golang-docs	1.25.10-1.module_el8.10.0+4187+c45165c4 · AlmaLinux:8	Package registry (OSV)
almalinux:golang-misc	1.25.10-1.module_el8.10.0+4187+c45165c4 · AlmaLinux:8	Package registry (OSV)
almalinux:golang-race	1.25.10-1.module_el8.10.0+4187+c45165c4 · AlmaLinux:8	Package registry (OSV)
almalinux:golang-src	1.25.10-1.module_el8.10.0+4187+c45165c4 · AlmaLinux:8	Package registry (OSV)
almalinux:golang-tests	1.25.10-1.module_el8.10.0+4187+c45165c4 · AlmaLinux:8	Package registry (OSV)
debian:golang-1.25	1.25.10-1 · Debian:14	Package registry (OSV)
debian:golang-1.26	1.26.3-1 · Debian:14	Package registry (OSV)
Go:toolchain	1.25.10	Package registry (OSV)
Go:toolchain	1.26.3	Package registry (OSV)
opensuse:go1.25	1.25.10-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
opensuse:go1.26	1.26.3-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
opensuse:opa	1.16.2-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
red hat:delve	0:1.25.2-1.module+el8.10.0+23746+9db33b5e · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:delve-debuginfo	0:1.25.2-1.module+el8.10.0+23746+9db33b5e · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:delve-debugsource	0:1.25.2-1.module+el8.10.0+23746+9db33b5e · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:go-toolset	0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:golang	0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:golang-bin	0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:golang-docs	0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:golang-misc	0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:golang-race	0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:golang-src	0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:golang-tests	0:1.25.10-1.module+el8.10.0+24308+5c4a16b7 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Mundur (https://github.com/M0nd0R)

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
A user must open a link or visit a page.
Special conditions such as timing or configuration are required.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: Required
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-347 · Improper Verification of Cryptographic Signature

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

nvd-secondary

Root cause

The verifier takes the algorithm to verify with from the token’s own header. Untrusted data ends up deciding its own verification rule.

The bug in code

The whole CWE-347 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const claims = jwt.verify(token, publicKey);

Fixed

1const claims = jwt.verify(token, publicKey, {
2  algorithms: ["RS256"],
3  issuer: "https://id.example.com",
4  audience: "portal",
5});

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 10:09 PM UTC

For records you follow, these changes also arrive as notifications. →

References

go.dev/cl/775321

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records