cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-69247: 0.27% estimated exploitation activity in the next 30 days; percentile 19.90 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary pkcs7decryptder, pkcs7decryptpem, and pkcs7decryptsmime 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,…

Published by the source

3 Aug 2026, 21:17 UTC

Last modified by the source

3 Aug 2026, 21:18 UTC

Source last checked

26 Oct 2026, 13:50 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-g6cj-pr64-35w5

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# Patch Next advisory brief: CVE-2026-69247

Advisory: cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing
IDs: CVE-2026-69247, GHSA-g6cj-pr64-35w5
Record: https://patchnext.com/advisories/cve-2026-69247 (revision 1, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: cryptography 50.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI cryptography: affected >= 44.0.0, < 50.0.0; fixed in 50.0.0

## Suggested inspection (read-only)
- `python -m pip show cryptography`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on cryptography.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-g6cj-pr64-35w5 (GitHub-reviewed advisory GHSA-g6cj-pr64-35w5 lists affected ranges: PyPI cryptography >=44.0.0 <50.0.0)

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