CVE-2023-50781 is a high severity timing side channel in M2Crypto RSA decryption, scored 7.5. It may let a remote attacker decrypt captured TLS messages on servers that use RSA key exchange. The sources do not confirm a fixed version, so apply your vendor update and prefer ECDHE.
What's affected
The NVD record lists Red Hat Enterprise Linux 8 and 9 and Red Hat Update Infrastructure among the affected products, and names the m2crypto component. Red Hat's page does not state affected product versions or a fix status. The Bugzilla entry 2254426 is the place for those details.
NVD and Red Hat both give 7.5 (High) with the vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Red Hat marks its score as preliminary and shows no separate impact rating. The record was published on 2024-02-05 and also links a Siemens advisory, which was not fetched here.
Red Hat describes the flaw as a Bleichenbacher style timing issue in the RSA decryption API, and as an incomplete fix for CVE-2020-25657. Red Hat says mitigation is either not available or does not meet its criteria for ease of use and stability.
How to check if you're exposed
Check whether M2Crypto is installed and which build:
pip show M2Crypto
rpm -q m2crypto python3-m2crypto
Then compare with your vendor's security errata for this CVE. The sources here do not give a fixed version, so rely on the vendor tracker.
The flaw matters most where M2Crypto is used inside a TLS server that accepts RSA key exchange. A client side script that never performs RSA decryption of attacker supplied data is unlikely to be reachable.
What to do now
- Inventory systems and applications that use M2Crypto and note the version.
- Read the Red Hat errata and Bugzilla entry for fixed packages and apply the update.
- Disable RSA key exchange cipher suites in TLS servers that use the library, preferring ECDHE suites.
- Rebuild container images that bundle the Python package.
- Check the Siemens advisory if you run Siemens products listed in the record.
Why it matters
The weakness is an observable discrepancy, CWE-203. In a Bleichenbacher style attack, a server that reacts differently to correctly and incorrectly padded RSA messages lets an observer learn about the plaintext by sending many queries and measuring differences, including timing.
Here the timing difference in the RSA decryption call is the leak. This family of flaws has been patched several times, and Red Hat describes this one as an incomplete fix for an earlier CVE.
The record shows no CISA Known Exploited Vulnerabilities listing, and the fetched page does not report exploitation in the wild.
Quick check
Is there a fixed version?
The sources fetched do not state one. Check your vendor errata.
What is the simplest hardening step?
Turn off RSA key exchange cipher suites in TLS servers and prefer ECDHE, as the flaw affects servers that use RSA key exchange.
Sources
Last reviewed: 19 October 2026.
