Raw vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-21861 is a critical-severity OS Command Injection (CWE-78) vulnerability in Basercms Basercms. Its CVSS base score is 9.1 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Command and Scripting Interpreter (T1059); ranked in the top 18% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-21861 is an OS command injection vulnerability (CWE-78) in baserCMS, an open-source website development framework. The issue affects versions prior to 5.2.3 and exists in the core update functionality, where user-controlled input is passed directly to the exec() function without sufficient validation or escaping, allowing arbitrary command execution on the server.
An authenticated administrator with high privileges (PR:H) can exploit this vulnerability remotely over the network (AV:N) with low attack complexity (AC:L) and no user interaction (UI:N). Exploitation changes scope (S:C) and results in high impacts across confidentiality, integrity, and availability (C:H/I:H/A:H), yielding a CVSS v3.1 base score of 9.1 and enabling full server compromise through arbitrary OS command execution.
The vulnerability is patched in baserCMS version 5.2.3. Mitigation involves upgrading to this version or later. Additional details are provided in advisories from https://basercms.net/security/JVN_20837860, https://github.com/baserproject/basercms/releases/tag/5.2.3, and https://github.com/baserproject/basercms/security/advisories/GHSA-qxmc-6f24-g86g.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-17255
Vulnerability Data
baserCMS is a website development framework. Prior to version 5.2.3, baserCMS contains an OS command injection vulnerability in the core update functionality. An authenticated administrator can execute arbitrary OS commands on the server due to improper handling of user-controlled input…
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that is directly passed to exec() without sufficient validation or escaping. This issue has been patched in version 5.2.3.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.2.5V1.2.8V15.2.5
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover missing or incorrect command sanitization during development.
Input validation directly neutralizes or rejects special characters that would otherwise alter OS command structure.
Least privilege reduces the permissions available to any process that could be subverted by injected commands.
Least functionality restricts available OS commands and interpreters, limiting the blast radius of injection.
Secure engineering principles require proper neutralization of untrusted input before command construction.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
PR.PS-06's SDLC practices directly require secure coding and input handling that blocks command-injection defects, yet the single broad outcome leaves many specific neutralization vectors and verification gaps unaddressed.
Routine patching/maintenance can remediate known command-injection CVEs in dependencies (partial forward) but does nothing to stop developers from introducing improper neutralization in custom code (none reverse).
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing and code review target insecure use of operating-system command interfaces, catching command-injection flaws introduced during development.