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The vulnerability stems from a missing cryptographic “key commitment” mechanism in the S3 Encryption Client for Ruby when using the “Instruction File” feature. In envelope encryption, data is encrypted with a unique data key, which is itself encrypted (becoming an Encrypted Data Key or EDK) and stored separately. Without key commitment, a single ciphertext can be decrypted into two different plaintexts using two different keys. An attacker with write permissions to the S3 bucket can exploit this by replacing the legitimate instruction file containing the EDK with a malicious one containing a rogue EDK. This rogue EDK is crafted so that the original ciphertext decrypts to an attacker-chosen plaintext. Subsequent decryption operations by the client will use the swapped EDK, returning manipulated data without detection, constituting an “Invisible Salamanders” attack.
Platform: AWS SDK Ruby
Version: <= 1.207.0
Vulnerability: Missing Key Commitment
Severity: Medium
Date: 2025-12-17
Prediction: 2025-12-17
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` Check current SDK version in Gemfile.lock`
`grep -E ‘aws-sdk-s3|aws-sdk-core’ Gemfile.lock`
` Upgrade the SDK to the patched version`
`bundle update aws-sdk-s3`
` Example of initializing a vulnerable client with instruction file`
`client = Aws::S3::Encryption::Client.new(
key_provider: my_key_provider,
envelope_location: :instruction_file
)`
How Exploit:
- Attacker gains write access to the target S3 bucket.
- A legitimate object is encrypted using a vulnerable client (
<=1.207.0) withenvelope_location: :instruction_file. - Attacker creates a rogue Encrypted Data Key that decrypts the existing ciphertext to malicious plaintext.
- Attacker overwrites the original `.instruction` file in the bucket with a new one containing the rogue EDK.
- When a user decrypts the object, the client fetches the rogue EDK and decrypts the data to the attacker’s plaintext.
Protection from this CVE
Upgrade to version `1.208.0` or later.
Avoid using `:instruction_file` for envelope location.
Apply strict least-privilege IAM policies.
Monitor S3 `PutObject` API calls for instruction files.
Impact
Compromises data integrity.
No direct confidentiality loss.
Enables undetected data tampering.
Violates cryptographic safety guarantees.
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Sources:
Reported By: github.com
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