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How the CVE works:
The vulnerability CVE-2022-39327 exists in the go-tuf implementation of The Update Framework (TUF). It specifically affects the metadata.VerifyDelegate function, which handles verification of delegated metadata roles. TUF uses metadata files signed by trusted keys to secure software updates, with thresholds defining the minimum number of signatures required. The flaw occurs because the VerifyDelegate function does not validate the configured threshold value before comparison. If a TUF repository is compromised or misconfigured, an attacker can set the threshold to 0 or a negative value in the metadata. During verification, the function checks if the number of valid signatures is greater than or equal to the threshold. With a threshold of 0, this condition always passes, even with zero valid signatures. Similarly, a negative threshold always passes since signature counts are non-negative. This effectively disables signature verification, allowing unauthorized modifications to metadata files without detection. Attackers can exploit this to tamper with metadata, such as altering target file hashes to point to malicious software packages. Clients fetching updates from the compromised repository will accept these malicious changes, leading to code execution and supply chain compromise. The vulnerability is critical because it undermines TUF’s security model, enabling widespread attacks on software distribution systems.
Platform: go-tuf
Version: < v2.3.1
Vulnerability: Improper threshold validation
Severity: Critical
Date: 2022-10-01
Prediction: Patch 2022-10-01
What Undercode Say:
Analytics:
- Check version: `go list -m all | grep go-tuf`
– Vulnerable code snippet:
func VerifyDelegate(threshold int) bool {
if len(signatures) >= threshold {
return true
}
return false
}
– Test threshold: `cat metadata.json | grep threshold`
how Exploit:
- Set threshold zero.
- Modify metadata maliciously.
- Bypass signature verification.
Protection from this CVE:
- Upgrade to v2.3.1.
- Validate threshold positivity.
- Audit repository configurations.
Impact:
- Disables signature checks.
- Allows metadata tampering.
- Compromises software updates.
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Sources:
Reported By: github.com
Extra Source Hub:
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