CVE-2026-69247 cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing
Attackers can exploit a Bleichenbacher oracle in PKCS#7 decryption to recover content-encryption keys, compromising data confidentiality in applications processing untrusted S/MIME or PKCS#7 data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-69247?
CVE-2026-69247 is a high-severity vulnerability in pyca cryptography, published on 3 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
cryptography is a package designed to expose cryptographic primitives and recipes to Python developers. From 44.0.0 until 50.0.0, 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. Decryption ran as RSA PKCS#1 v1.5 decrypt of encryptedKey, build an AES cipher from the result, then AES-CBC decrypt and PKCS#7 unpad. Invalid RSA padding, a valid padding with a bad key length, a correct length with a wrong key, and the real key each failed or succeeded differently. Case 1 is reachable only where the linked library lacks implicit rejection: OpenSSL 3.0 and 3.1, LibreSSL, and BoringSSL. Exploitation requires a service that auto-decrypts untrusted EnvelopedData matching the victim certificate and answers adaptively at high volume, such as an S/MIME gateway or mail filter. This issue is fixed in 50.0.0.
Which versions are affected by CVE-2026-69247?
3 open source packages ship an affected version, including cryptography.
| Package | Affected | Fixed in |
|---|---|---|
cryptography PyPI | From 44.0.0 | 50.0.0 |
cryptography PyPI | From 44.0.0 | 50.0.0 |
cryptography PyPI | From 44.0.0 | 50.0.0 |
How do I fix CVE-2026-69247?
Upgrade cryptography to 50.0.0 or later.
Is CVE-2026-69247 being exploited?
There is no known exploitation of CVE-2026-69247 in the wild and no public exploit code.
Sources
Also known as CLEANSTART-2026-SR43312, CLEANSTART-2026-WC97010, CLEANSTART-2026-XM41413, CLEANSTART-2026-XM81599, DEBIAN-CVE-2026-69247, ECHO-896e-5bc2-1efe and 41 more.