Quick answer
Direct answer
Risk scores
| CVSS metric | What it means |
|---|---|
| Attack vector (AV:N) | Network: reachable remotely |
| Attack complexity (AC:H) | High complexity |
| Attack requirements (AT:P) | Attack requirements present |
| Privileges required (PR:N) | No privileges required |
| User interaction (UI:N) | No user interaction |
| Confidentiality (VC:H) | High confidentiality impact |
| Integrity (VI:H) | High integrity impact |
| Availability (VA:H) | High availability impact |
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
About Pyopenssl
CVE-2026-27459 affects Pyopenssl, a product from Pyopenssl. Before acting, confirm where Pyopenssl runs in your estate, who owns it and whether it is reachable from the internet, because exposure decides real risk more than the score alone.
What the flaw is
In plain terms: 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.
The weakness class is Classic Buffer Overflow. Data is copied into a buffer without checking its size.
Based on its CVSS vector, the flaw can be reached over the network, needs no login, and needs no user interaction. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.
Affected versions and timeline
| Field | Detail |
|---|---|
| Product | Pyopenssl |
| Affected versions | Pyopenssl from 22.0.0 before 26.0.0 |
| Published | Mar 18, 2026 |
| Last modified | Sep 10, 2026 |
| Added to CISA KEV | Not listed |
| Assigning CNA | security-advisories@github.com |
How to detect it
- Inventory every instance of Pyopenssl and record the running version against the affected range above.
- Check external attack surface scans for internet facing instances of the component.
- Review logs on affected systems for unusual requests, errors or new processes around the vulnerable function.
- Confirm with an authenticated vulnerability scan once your scanner has a check for this CVE.
How to fix it
- Apply the fixed version of Pyopenssl named in the vendor advisory.
- If patching must wait, restrict network access to the affected service and put it behind authentication or a web application firewall rule.
- Rescan after the change to prove the exposure is gone, then close the ticket.
CTEM action plan
| CTEM stage | What to do for this CVE |
|---|---|
| Scope | Add every business service that depends on Pyopenssl to the current CTEM cycle. |
| Discover | Find all instances, including shadow and cloud deployments, and record versions and exposure. |
| Prioritize | Rank using EPSS and CVSS together with asset exposure and business impact. |
| Validate | Confirm the flaw is reachable and exploitable in your environment and that compensating controls work. |
| Mobilize | Assign the fix to the asset owner with a due date matched to the priority, then verify closure. |
CWE References
- CWE-120: Classic Buffer Overflow More CVEs with this weakness
- CWE-120: Classic Buffer Overflow More CVEs with this weakness
Technical References
- ▸NVD entry
- ▸CVE.org record
- ▸GitHub repository reference
- ▸Fix commit on GitHub
- ▸GitHub Security Advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
- ▸Red Hat security advisory
Frequently asked questions
Related CVEs
Out-of-bounds Write, Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') vulnerability in azerothcore azerothcore-wotlk (deps/zlib modules). This vulnerability is associated with program files inflate.C. This issue affects azerothcore-wotlk: through v4.0.0.
In DeviceId of DeviceId.java, there is a possible desync in persistence due to a missing bounds check. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.
Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Tenda AC6 15.03.05.16_multi is vulnerable to Buffer Overflow in the formSetCfm function via the funcname, funcpara1, and funcpara2 parameters.
An issue was discovered in Tenda W20E V4.0br_V15.11.0.6. Attackers may exploit the vulnerability by controlling the value of `picName`. When this value is used in `sprintf` without validating variable sizes, it could lead to a buffer overflow vulnerability.
An issue was discovered in Tenda W20E V4.0br_V15.11.0.6. Attackers may exploit the vulnerability by specifying the value of `userInfo`. When `userInfo` is passed into the `addAuthUser` function and processed by `sscanf` without size validation, it could lead to buffer overflow.
Earn your free CTEM certification.
Learn to scope, prioritize, validate and mobilize fixes for CVEs like CVE-2026-27459 with a free CTEM certification.
Beginner / Practitioner / Program Leader
Explore certifications