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.
CVE-2026-27459
CRITICALNVD 9.89.8
EchelonGraph scoreLOW confidence
This critical-severity CVE scores 9.8 under NVD CVSS v3. EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: nvd
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 9.8Exploit: NoneExposed: 0
A fix is available — apply it.
- CVSS v3
- 9.8
- EG Score
- 9.8(low)
- EPSS
- 48.8%
- KEV
- Not listed
Published
March 18, 2026
Last Modified
July 1, 2026
Advisory Details (10)
Auto-updated Jul 3, 2026Patch available. Sources: github, redhat, github_commit.
redhat Patch Available
redhat Patch Available
redhat Patch Available
redhat Patch Available
redhat Patch Available
redhat Patch Available
redhat Patch Available
github Patch Available
Buffer overflow if DTLS cookie callback returned too long of a value · Advisory · pyca/pyopenssl · GitHub
https://github.com/pyca/pyopenssl/security/advisories/GHSA-5pwr-322w-8jr4github_commit
commit 57f09bb4bb05 (pyca/pyopenssl)
Fix landed in pyca/pyopenssl commit 57f09bb4bb05 — awaiting tagged release
https://github.com/pyca/pyopenssl/commit/57f09bb4bb051d3bc2a1abd36e9525313d5cd408generic
pyopenssl/CHANGELOG.rst at 358cbf29c4e364c59930e53a270116249581eaa3 · pyca/pyopenssl · GitHub
https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rstVendor Advisories for CVE-2026-27459(18)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- RHSA-2026:24853Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Quay 3.15.5
- RHSA-2026:22465Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Quay 3.17.2
- CVE-2026-27459Microsoft Security Response Center (MSRC)High
pyOpenSSL DTLS cookie callback buffer overflow
- RHSA-2026:21017Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Quay 3.14.8
- RHSA-2026:19375Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Quay 3.16.4
- RHSA-2026:14874Red Hat Product SecurityHigh
Red Hat Security Advisory: Satellite 6.16.8 Async Update
- RHSA-2026:14873Red Hat Product SecurityHigh
Red Hat Security Advisory: Satellite 6.17.8 Async Update
- RHSA-2026:14835Red Hat Product SecurityHigh
Red Hat Security Advisory: Satellite 6.18.5 Async Update
- +10 more
Patch Availability(16)
| Vendor / Ecosystem | Fixed in / Patch | Released | Source |
|---|---|---|---|
| redhat | quay/quay-rhel8:1780891395 | 2026-06-09 | redhat |
| redhat | quay/quay-rhel9:1779922205 | 2026-06-02 | redhat |
| redhat | quay/quay-rhel8:1779689392 | 2026-05-26 | redhat |
| redhat | quay/quay-rhel9:1779204086 | 2026-05-19 | redhat |
| redhat | python3.12-pyOpenSSL-0:26.0.0-2.el9pc | 2026-05-07 | redhat |
| redhat | python-pyOpenSSL-0:25.1.0-0.3.el9pc | 2026-05-07 | redhat |
| redhat | python-pyOpenSSL-0:24.1.0-2.el9pc | 2026-05-07 | redhat |
| redhat | python3.12-pyOpenSSL-0:26.0.0-1.el9ap | 2026-05-04 | redhat |
| redhat | ansible-automation-platform-25/lightspeed-rhel8:1777403872 | 2026-05-04 | redhat |
| redhat | ansible-automation-platform-26/platform-resource-runner-rhel9:1777390333 | 2026-05-04 | redhat |
| redhat | quay/quay-rhel8:1776782369 | 2026-04-30 | redhat |
| redhat | quay/quay-rhel8:1776736910 | 2026-04-29 | redhat |
| redhat | quay/quay-rhel8:1776752646 | 2026-04-29 | redhat |
| redhat | python-pyOpenSSL-0:24.1.0-2.el8ui | 2026-04-27 | redhat |
| redhat | rhtas/model-transparency-rhel9:1775815407 | 2026-04-16 | redhat |
| redhat | pyopenssl-main-26.0.0-1.1.hum1 | 2026-04-09 | redhat |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(1 across 1 ecosystem)
PyPI(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| pyopenssl | 22.0.0 ... 25.3.0 (15 versions) | 26.0.0 | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 11× in last 7d / 14× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-06 16:27 UTCEPSS rescore
- 2026-07-06 16:27 UTCEPSS rescore
- 2026-07-06 02:23 UTCEPSS rescore
- 2026-07-06 02:23 UTCEPSS rescore
- 2026-07-05 02:30 UTCEPSS rescore
- 2026-07-04 06:31 UTCEPSS rescore
- 2026-07-04 06:31 UTCEPSS rescore
- 2026-07-01 15:06 UTCEPSS rescore
- 2026-07-01 15:06 UTCEPSS rescore
- 2026-06-30 23:22 UTCEPSS rescore
- 2026-06-30 23:22 UTCEPSS rescore
- 2026-06-30 04:33 UTCEG score recompute
- 2026-06-30 04:33 UTCVendor advisory
- 2026-06-30 04:31 UTCNVD updatefirst tracked
Frequently asked(5)
What is CVE-2026-27459?
CVE-2026-27459 is a critical vulnerability published on March 18, 2026. 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 setcookiegenerate_callback returned a cookie value greater than 256 bytes, pyOpenSSL would overflow an OpenSSL provided buffer. Starting in version…
When was CVE-2026-27459 disclosed?
CVE-2026-27459 was first published in the National Vulnerability Database on March 18, 2026, with the most recent update on July 1, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-27459 actively exploited?
CVE-2026-27459 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 48.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-27459?
CVE-2026-27459 has a CVSS v3 base score of 9.8 (NVD). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-27459?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-27459, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-27459
Is Your Infrastructure Affected by CVE-2026-27459?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.