CVE-2026-27459: pyOpenSSL is a Python wrapper around the OpenSSL library

This month

CRITICAL 9.8REMOTEWATCHLISTUPGRADE

CVE-2026-27459 is a critical-severity flaw (CVSS 9.8) 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 22.0.0 and prior to version 26.0.0, if a user provided callback to `set_cookie_generate_callback` returned a cookie value greater than 256 bytes, pyOpenSSL would overflow an OpenSSL provided buffer. Starting in version 26.0.0, cookie values that are too long are now rejected.

Why this priority

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

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Weakness	CWE-120
Published	2026-03-18
Last modified	2026-09-10

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

Last updated 2026-09-10 · 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
2026-09-10 13:17 UTCUpdated Record last modified

pyopenssl pyopenssl UPGRADE

Affected: >= 22.0.0 and < 26.0.0

Fixed in: 26.0.0

Safe to downgrade to: a release before 22.0.0

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 22.0.0 (Debian / Ubuntu)

apt-cache madison pyopenssl sudo apt install pyopenssl=<VERSION_BEFORE_22.0.0> 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_22.0.0> 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.

Exact fixes by distribution

Python (pip) · pyopenssl · FIXED · 26.0.0 · vulnerable: >= 22.0.0, < 26.0.0 · source

pip install --upgrade "pyopenssl>=26.0.0" pip show pyopenssl

Fedora 46 · wordpress · FIXED · 7.1.4-1.fc46 · FEDORA-2026-907394725e · source

sudo dnf upgrade --advisory=FEDORA-2026-907394725e

Fedora ELN · rhc · FIXED · 0.3.15-1.eln159 · FEDORA-2026-1cd9f35750 · source

sudo dnf upgrade --advisory=FEDORA-2026-1cd9f35750

Debian 12 · pyopenssl · NO FIX YET

Debian 13 · pyopenssl · FIXED · 25.0.0-1+deb13u1

sudo apt update && sudo apt install --only-upgrade pyopenssl dpkg --compare-versions "$(dpkg-query -W -f='${Version}' pyopenssl)" ge "25.0.0-1+deb13u1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 6 · pyOpenSSL · NOT AFFECTED

RHEL 7 · pyOpenSSL · NOT AFFECTED

RHEL 8 · pyOpenSSL · NOT AFFECTED

Alpine 3.23 · py3-openssl · FIXED · py3-openssl-26.1.0-r0

apk add --upgrade py3-openssl apk info -v py3-openssl

Alpine 3.24 · py3-openssl · FIXED · py3-openssl-26.1.0-r0

apk add --upgrade py3-openssl apk info -v py3-openssl

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-2026-27459?

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

Is CVE-2026-27459 being exploited?

CVE-2026-27459 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-2026-27459 affect?

CVE-2026-27459 affects pyopenssl. Severity is critical (CVSS 9.8). pyOpenSSL is a Python wrapper around the OpenSSL library. Starting in version 22.0.0 and prior to version 26.0.0, if a user provided callback to `set_cookie_generate_callback` returned a cookie value greater than 256 bytes, pyOpenSSL would

How urgent is CVE-2026-27459?

Priority 58/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

OpenSSL vulnerabilities · Python vulnerabilities

Related CVEs

CVE-2026-27448 MEDIUM 5.3 UPGRADE pyOpenSSL is a Python wrapper around the OpenSSL library

References

← Back to latest CVEs