CVE-2026-27448 pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback
Attackers can bypass TLS security checks if a custom server name callback raises an unhandled exception, allowing unauthorized connections.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27448?
CVE-2026-27448 is a low-severity vulnerability in pyca pyopenssl, published on 17 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
pyOpenSSL is a Python wrapper around the OpenSSL library. Starting in version 0.14.0 and prior to version 26.0.0, if a user provided callback to `set_tlsext_servername_callback` raised an unhandled exception, this would result in a connection being accepted. If a user was relying on this callback for any security-sensitive behavior, this could allow bypassing it. Starting in version 26.0.0, unhandled exceptions now result in rejecting the connection.
Weakness: CWE-636
Which versions are affected by CVE-2026-27448?
3 open source packages ship an affected version, including pyopenssl. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pyopenssl PyPI | From 0.14 | 26.0.0 |
pyopenssl PyPI | From 0.14.0 | 26.0.0 |
pyopenssl PyPI | From 0.14.0 | 26.0.0 |
Linux distribution packages (6)
python-pyOpenSSL SUSE:Linux Enterprise Micro 5.2 | All versions | 19.0.0-150300.3.3.1 |
python3-pyOpenSSL SUSE:Linux Enterprise Micro 5.3 | All versions | 21.0.0-150400.22.1 |
python3-pyOpenSSL SUSE:Linux Enterprise Micro 5.4 | All versions | 21.0.0-150400.22.1 |
python3-pyOpenSSL SUSE:Linux Enterprise Micro 5.5 | All versions | 21.0.0-150400.22.1 |
python3-pyOpenSSL SUSE:Linux Enterprise Module for Basesystem 15 SP7 | All versions | 21.0.0-150400.22.1 |
python-pyOpenSSL SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5 | All versions | 17.1.0-4.32.1 |
Products include Pyopenssl Pyopenssl.
How do I fix CVE-2026-27448?
Upgrade pyopenssl to 26.0.0 or later.
Is CVE-2026-27448 being exploited?
There is no known exploitation of CVE-2026-27448 in the wild and no public exploit code.
Other vulnerabilities in pyca pyopenssl
Sources
Also known as AZL-80031, BELL-CVE-2026-27448, CLEANSTART-2026-FW34040, CLEANSTART-2026-KN51802, CLSA-2026-1776098295, CLSA-2026-1779181743 and 19 more.