CVE-2026-56864Network attack vector

Malicious module injection via unvalidated Lookup hashes

Published Aug 13, 2026 · Updated Aug 13, 2026

Checksum verification bypass in Go command and golang.org/x/mod/sumdb allows remote attackers to inject malicious module content. Client.Lookup searched the entire server record and returned requested-module hashes from an unauthenticated signed-tree extension rather than only lines validated by tlog.ParseRecord. Exploitation requires a colluding GOPROXY and GOSUMDB, or a proxy holding the checksum-database key, and can persist attacker-controlled code in the local module cache.

CVSS severity7.5
High
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Checksum verification bypass in Go command and golang.org/x/mod/sumdb allows remote attackers to inject malicious module content. Client.Lookup searched the entire server record and returned requested-module hashes from an unauthenticated signed-tree extension rather than only lines validated by tlog.ParseRecord. Exploitation requires a colluding GOPROXY and GOSUMDB, or a proxy holding the checksum-database key, and can persist attacker-controlled code in the local module cache.

The record

CVE
CVE-2026-56864
Published
Aug 13, 2026
Updated
Aug 13, 2026
Vendor
Google Cloud
Product
Go command
Classifications
CWE-347, T1195.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 13, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <1.25.13
  2. Affected versionversion=1.26.0-0 <1.26.6
  3. Affected versionversion=1.27.0-0 <1.27.0-rc.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Go commandversion=0 <1.25.13; version=1.26.0-0 <1.26.6; version=1.27.0-0 <1.27.0-rc.3
golang.org/x/mod · golang.org/x/mod/sumdbversion=0 <0.40.0

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
T1195.001Compromise Software Dependencies and Development Tools

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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