CVE-2026-21902
Juniper Junos Os Evolved 25.4
Raw vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:L/E:X/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:Y/R:U/V:X/RE:M/U:RedSummary
CVE-2026-21902 is a critical-severity Incorrect Permission Assignment for Critical Resource (CWE-732) vulnerability in Juniper Junos Os Evolved. Its CVSS base score is 9.3 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Credentials In Files (T1552.001); ranked in the top 3% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-6 (Least Privilege) — 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-2026-21902 is an Incorrect Permission Assignment for Critical Resource vulnerability (CWE-732) in the On-Box Anomaly detection framework of Juniper Networks Junos OS Evolved on PTX Series routers. Published on 2026-02-25, it carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H). The flaw affects Junos OS Evolved 25.4 versions prior to 25.4R1-S1-EVO and 25.4R2-EVO; it does not impact versions before 25.4R1-EVO or standard Junos OS.
An unauthenticated, network-based attacker can exploit this vulnerability by accessing the On-Box Anomaly detection framework, which is enabled by default with no configuration required and incorrectly exposed on an externally facing port instead of being limited to internal processes over the internal routing instance. Successful exploitation allows the attacker to manipulate the service and execute arbitrary code as root, resulting in complete control of the device.
Juniper's security advisories JSA107128 and support portal documentation at https://kb.juniper.net/JSA107128 and https://supportportal.juniper.net/JSA107128 outline mitigation steps, including upgrading to patched releases such as 25.4R1-S1-EVO or 25.4R2-EVO. A proof-of-concept exploit script is publicly available on GitHub at https://github.com/watchtowrlabs/watchTowr-vs-JunosEvolved-CVE-2026-21902/blob/main/watchTowr-vs-JunosEvolved-CVE-2026-21902.py.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8693
Vulnerability Data
An Incorrect Permission Assignment for Critical Resource vulnerability in the On-Box Anomaly detection framework of Juniper Networks Junos OS Evolved on PTX Series allows an unauthenticated, network-based attacker to execute code as root. The On-Box Anomaly detection framework should only…
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be reachable by other internal processes over the internal routing instance, but not over an externally exposed port. With the ability to access and manipulate the service to execute code as root a remote attacker can take complete control of the device. Please note that this service is enabled by default as no specific configuration is required. This issue affects Junos OS Evolved on PTX Series: * 25.4 versions before 25.4R1-S1-EVO, 25.4R2-EVO. This issue does not affect Junos OS Evolved versions before 25.4R1-EVO. This issue does not affect Junos OS.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 7 hardening rules · 4 OS baselines
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Mitigating Controls (NIST 800-53 r5) AI
Enforces the access control policy that defines permissions on resources, thereby stopping incorrect assignments from remaining exploitable.
Directly requires assignment of only the minimum necessary permissions, preventing overly broad grants on critical resources.
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.
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.
By requiring owners to determine and document the exact permissions needed for each asset, the control reduces the likelihood that default or overly permissive file and resource permissions will be left in place.
Documented provisioning and revocation procedures reduce the chance that critical resources retain overly permissive default or leftover permissions after personnel changes.
Documented authorization, expiry rules, and audit logging of privileged accounts make it harder for critical resources to retain overly permissive or stale permission assignments.
Requiring explicit configuration of access controls and permissions for files, applications and services counters the assignment of overly permissive default or incorrect file-system rights.
Enforcing differentiated permissions on the source-code repository and program listings stops the assignment of overly broad default or inherited permissions to critical resources.
By defining and enforcing secure permission settings in configuration templates, the control reduces the likelihood that critical resources receive incorrect permission assignments.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (1 rule)
- V-248577 OL 8 must enable kernel parameters to enforce Discretionary Access Control (DAC) on symlinks. prevents CWE-732
Windows Server 2016 (2 rules)
- V-224972 Active Directory Group Policy objects must have proper access control permissions. prevents CWE-732
- V-224831 Local volumes must use a format that supports NTFS attributes. prevents CWE-732
Windows Server 2019 (2 rules)
- V-205741 Windows Server 2019 Active Directory Group Policy objects must have proper access control permissions. prevents CWE-732
- V-205663 Windows Server 2019 local volumes must use a format that supports NTFS attributes. prevents CWE-732
Windows Server 2022 (2 rules)
- V-254393 Windows Server 2022 Active Directory Group Policy objects must have proper access control permissions. prevents CWE-732
- V-254250 Windows Server 2022 local volumes must use a format that supports NTFS attributes. prevents CWE-732