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CVE Record

CVE-2026-27459: pyOpenSSL DTLS cookie callback buffer overflow

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.

HighCVSS 8.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in pyOpenSSL can corrupt memory when certain DTLS cookie callbacks return oversized cookie values. The issue affects versions 22.0.0 through before 26.0.0. It is high severity because successful exploitation could affect confidentiality, integrity, and availability, but the published vector rates attack complexity as high.

Executive priority

Prioritize remediation for externally reachable DTLS services or products embedding affected pyOpenSSL versions. The issue is high severity, but evidence provided does not support emergency active-exploitation handling.

Technical view

In affected pyOpenSSL versions, a user-supplied set_cookie_generate_callback result longer than 256 bytes could overflow an OpenSSL-provided buffer. Version 26.0.0 rejects oversized cookie values. The CVSS 3.1 score is 8.1 with network attack vector, no privileges, no user interaction, and high complexity.

Likely exposure

Exposure is most likely in Python services using pyOpenSSL 22.0.0 to before 26.0.0 with DTLS cookie generation callbacks. General pyOpenSSL dependency alone may not mean the vulnerable callback path is reachable.

Exploitation context

The source bundle does not show KEV listing or cited active exploitation. The CVSS vector indicates remote reachability but high attack complexity. Treat internet-facing DTLS services using affected callback behavior as higher priority.

Researcher notes

Key constraints are the affected version range and the specific callback behavior. Validate reachability before broad impact claims. Avoid assuming all pyOpenSSL consumers are exploitable without evidence that DTLS cookie generation callbacks are used.

Mitigation direction

  • Upgrade pyOpenSSL to version 26.0.0 or later.
  • Apply relevant Red Hat security errata for downstream packaged deployments.
  • Inventory applications using pyOpenSSL DTLS cookie callbacks.
  • Follow vendor guidance if immediate upgrade is not possible.
  • Rebuild and redeploy affected Python environments after dependency updates.

Validation and detection

  • Check installed pyOpenSSL versions across runtime images and hosts.
  • Search code for set_cookie_generate_callback usage.
  • Confirm DTLS-facing services do not load affected pyOpenSSL versions.
  • Verify patched packages or pyOpenSSL 26.0.0+ in deployed artifacts.
  • Track Red Hat advisories for applicable platform package status.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-120: Exact CWE lookup

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cve · low confidence lookup

CVE-2026-27459 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
24Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9redhat-SADP
7.2CVSS 4.0HighCVSS: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——GitHub_M

Vulnerability scoring details

Base CVSS 4.0 score

7.2High
CVSS 4.0 vector shape for CVE-2026-27459Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: 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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPpyOpenSSL: DTLS cookie callback buffer overflow
other:Red Hat severity ratingcvssV3_1
  • 2026-03-18T00:01:41.404Z: Reported to Red Hat.
  • 2026-03-17T23:34:28.483Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
pycapyopenssl>= 22.0.0, < 26.0.0Listed
Weakness

CWE details

CWE-120

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-120 · source CWE mapping

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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