CVE-2026-27459
Description
A flaw was found in pyOpenSSL. The set_cookie_generate_callback callback function can be used to generate DTLS cookies. When the callback returns a cookie string or byte sequence longer than 256 bytes, a buffer overflow can be triggered due to a missing bounds checking before copying the data to a fixed-size buffer provided by the underlying OpenSSL library.
Statement
This flaw is only exploitable when an application using the pyOpenSSL library provides a custom callback to the set_cookie_generate_callback function. For the buffer overflow to occur, the callback function must return a cookie string or byte sequence longer than 256 bytes, limiting the exposure of this issue. Due to these reasons, this vulnerability has been rated with an important severity.
Mitigation
To mitigate this flaw, ensure the callback provided to the set_cookie_generate_callback function strictly limits the returned cookie string or byte sequence to under 256 bytes.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.1 | 9.8 | 8.1 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | Low | High |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | High | High | High |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Red Hat CVSS v3 Score Explanation
See the 'Statement' section for an explanation of the difference between the CVSS from Red Hat and NVD, specifically why the attack complexity metric is set to high.
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of the product's implicit security policy. This can often be used to subvert any other security service.
Availability
Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the product into an infinite loop.
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