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apko doesn't verify downloaded apk packages against APKINDEX checksum (package substitution possible)

High severity GitHub Reviewed Published Apr 23, 2026 in chainguard-dev/apko • Updated May 4, 2026

Package

gomod chainguard.dev/apko (Go)

Affected versions

< 1.2.7

Patched versions

1.2.7

Description

apko verifies the signature on APKINDEX.tar.gz but never compares individually downloaded .apk packages against the checksum recorded in the signed index. The checksum is parsed and available via ChecksumString(), and the downloaded package control hash is computed, but the two values are never compared in getPackageImpl(). Mismatched packages are silently accepted. An attacker who can substitute download responses (compromised mirror, HTTP repository, poisoned CDN cache) can install arbitrary packages into built images.

Fix: No fix available yet.

Acknowledgements

apko thanks Oleh Konko from 1seal for discovering and reporting this issue.

References

@antitree antitree published to chainguard-dev/apko Apr 23, 2026
Published to the GitHub Advisory Database May 4, 2026
Reviewed May 4, 2026
Last updated May 4, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS score

Weaknesses

Insufficient Verification of Data Authenticity

The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data. Learn more on MITRE.

Download of Code Without Integrity Check

The product downloads source code or an executable from a remote location and executes the code without sufficiently verifying the origin and integrity of the code. Learn more on MITRE.

CVE ID

CVE-2026-42575

GHSA ID

GHSA-hcwr-pq9g-rq3m

Source code

Credits

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