CVE-2026-27448: pyOpenSSL is a Python wrapper around the OpenSSL library

Routine

MEDIUM 5.3REMOTEWATCHLISTUPGRADE

CVE-2026-27448 is a medium-severity flaw (CVSS 5.3) affecting pyopenssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 connect

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 84%)
CISA exploited list	No
Weakness	CWE-636
Published	2026-03-18
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: pyopenssl

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-18 00:16 UTCPublished CVE record published
2026-06-17 10:27 UTCUpdated Record last modified

pyopenssl pyopenssl UPGRADE

Affected: >= 0.14 and < 26.0.0

Fixed in: 26.0.0

Safe to downgrade to: a release before 0.14

1. Check installed version

apt-cache policy pyopenssl || rpm -q pyopenssl || pyopenssl --version

2. UPGRADE to 26.0.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade pyopenssl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade pyopenssl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 0.14 (Debian / Ubuntu)

apt-cache madison pyopenssl sudo apt install pyopenssl=<VERSION_BEFORE_0.14> sudo apt-mark hold pyopenssl

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list pyopenssl sudo dnf downgrade pyopenssl-<VERSION_BEFORE_0.14> sudo dnf versionlock add pyopenssl

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-27448?

pyopenssl: upgrade to 26.0.0. Exact commands for each OS are on this page.

Is CVE-2026-27448 being exploited?

CVE-2026-27448 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-27448 affect?

CVE-2026-27448 affects pyopenssl. Severity is medium (CVSS 5.3). 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 connecti

How urgent is CVE-2026-27448?

Priority 33/100. Remotely exploitable, no login, no user action; On your watchlist

Software pages

OpenSSL vulnerabilities · Python vulnerabilities

Related CVEs

CVE-2026-27459 CRITICAL 9.8 UPGRADE pyOpenSSL is a Python wrapper around the OpenSSL library

References

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