Summary
cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing
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:
- invalid RSA padding →
Decryption failed - valid padding, bad key length →
Invalid key size (N) for AES., disclosingN - correct length, wrong key →
Invalid padding bytes. - 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 does not distinguish conforming
ciphertexts.
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.
Not addressed by this fix
EnvelopedData does not authenticate its content. Tampering withencryptedContent alone yields a CBC padding oracle that recovers plaintext at
roughly 256 queries per byte, without recovering any key, on every backend. This
is a property of PKCS#7 rather than of this implementation, cannot be fixed in
the library, and is now documented.
Credit
Reported by @X1AOxiang.
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Per RFC 3218, the content-encryption algorithm is now resolved before the
private key is used, so the expected key length is known in advance. If the RSA
decryption fails or recovers a key of the wrong length, a random key of the
expected length is substituted and decryption continues down an identical path.
All failures now report identically and perform the same work.
Frequently Asked Questions
- What is CVE-2026-69247? CVE-2026-69247 is a high-severity security vulnerability in cryptography (pip), affecting versions >= 44.0.0, < 50.0.0. It is fixed in 50.0.0.
- Which versions of cryptography are affected by CVE-2026-69247? cryptography (pip) versions >= 44.0.0, < 50.0.0 is affected.
- Is there a fix for CVE-2026-69247? Yes. CVE-2026-69247 is fixed in 50.0.0. Upgrade to this version or later.
- Is CVE-2026-69247 exploitable, and should I be worried? Whether CVE-2026-69247 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-69247 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-69247? Upgrade
cryptographyto 50.0.0 or later.