What is the CVSS score of CVE-2026-21899?

CVE-2026-21899 has a CVSS 3.1 base score of 4.7 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:L. EPSS exploitation probability: 0.0%.

Which versions of Cryptolib are affected by CVE-2026-21899?

CVE-2026-21899 presents moderate security risk, a out-of-bounds read vulnerability rated CVSS 4.7. Exploitation could cause memory corruption or application crashes.

Is there a public PoC exploit available for CVE-2026-21899?

Yes, a public proof-of-concept exploit is available for CVE-2026-21899. Prioritise patching immediately. EPSS: 0.0%.

Cryptolib CVE-2026-21899

MEDIUM

Out-of-bounds Read (CWE-125)

2026-01-10 security-advisories@github.com

Denial Of Service Cryptolib

4.7

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

4.7 MEDIUM

AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:L

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

High

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

Low

Lifecycle Timeline

Analysis Generated

Mar 12, 2026 - 21:54 vuln.today

PoC Detected

Jan 15, 2026 - 21:45 vuln.today

Public exploit code

CVE Published

Jan 10, 2026 - 01:16 nvd

MEDIUM 4.7

DescriptionGitHub Advisory

CryptoLib provides a software-only solution using the CCSDS Space Data Link Security Protocol - Extended Procedures (SDLS-EP) to secure communications between a spacecraft running the core Flight System (cFS) and a ground station. Prior to version 1.4.3, in base64urlDecode, padding-stripping dereferences input[inputLen - 1] before checking that inputLen > 0 or that input != NULL. For inputLen 0, this becomes an OOB read at input[-1], potentially crashing the process. If input NULL and inputLen == 0, it dereferences NULL - 1. This issue has been patched in version 1.4.3.

AnalysisAI

CryptoLib versions prior to 1.4.3 contain an out-of-bounds read vulnerability in the base64urlDecode function that dereferences memory before validating input parameters, potentially causing a denial of service in spacecraft communications secured by SDLS-EP. Affected systems running cFS with vulnerable CryptoLib versions could crash when processing malformed base64 input. …

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Vulnerability AssessmentAI

Risk Assessment	CVSS 4.7 (MEDIUM). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	An attacker could exploit this vulnerability to compromise the affected system.
Remediation	Fixed in version 1.4.3.. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. …

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CVE-2026-21899 vulnerability details – vuln.today

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