CVE-2026-69247 — cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing

Affected: pyca cryptography

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.

USN-8776-1 — python-cryptography vulnerabilities

Affected: Ubuntu:Pro:18.04:LTS: python-cryptography, Ubuntu:26.04:LTS: python-cryptography

It was discovered that python-cryptography incorrectly accepted objects with immutable buffers when performing certain cipher operations. This would result in corrupted output, contrary to expectations. This issue only affected Ubuntu 18.04 LTS. (CVE-2023-23931)

It was discovered that python-cryptography reported the outcome of decrypting PKCS#7 enveloped data in distinguishable ways, and with observable timing differences. A remote attacker could possibly use this issue to recover the key used to encrypt the message contents, and obtain sensitive information. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-69247)

Jack Lloyd discovered that python-cryptography incorrectly handled wildcard DNS names when enforcing the name constraints of a certificate authority. A remote attacker could possibly use this issue to have an invalid certificate chain accepted, and use names outside of the permitted ones. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-69248)

Samuel Judson discovered that python-cryptography incorrectly handled certificate chains that contained duplicate certificates. A remote attacker could possibly use this issue to cause python-cryptography to use excessive resources, leading to a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-69249)

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CVE-2026-69247 — cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing

USN-8776-1 — python-cryptography vulnerabilities