vulnerability / NVI-00015320 / Revision 1
cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing
GitHub lists this reviewed advisory for cryptography. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
cryptography
source listed>= 44.0.0, < 50.0.0
### Summary `pkcs7_decrypt_der`, `pkcs7_decrypt_pem`, and `pkcs7_decrypt_smime` reported the outcome of decrypting a `RecipientInfo`'s `encryptedKey` in several distinguishable ways, one of which disclosed the exact length recovered from the RSA operation. The same distinction was also observable by timing. An application that decrypts attacker-supplied `EnvelopedData` and reflects the outcome gives the attacker a Bleichenbacher oracle against the content-encryption key. Introduced in 44.0.0. Fixed in 50.0.0. ### Details Decryption ran as: RSA PKCS#1 v1.5 decrypt of `encryptedKey` → build an AES cipher from the result → AES-CBC decrypt and PKCS#7 unpad. Each stage failed differently, with no RFC 3218 mitigation: 1. invalid RSA padding → `Decryption failed` 2. valid padding, bad key length → `Invalid key size (N) for AES.`, disclosing `N` 3. correct length, wrong key → `Invalid padding bytes.` 4. the real key → plaintext Case 1 is reachable only where the linked library lacks implicit rejection: OpenSSL 3.0 and 3.1, LibreSSL, and BoringSSL. On OpenSSL 3.2+, used in our wheels, invalid padding instead returns a synthetic plaintext of pseudorandom length, so the error channel do
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
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04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-g6cj-pr64-35w5 ↗
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Public revision history
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- Revision 1 ·
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