CVE-2026-21916
Juniper Junos ≤ 23.2
Raw vector
CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:P/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:XSummary
CVE-2026-21916 is a high-severity UNIX Symbolic Link (Symlink) Following (CWE-61) vulnerability in Juniper Junos. Its CVSS base score is 7.0 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Path Interception (T1034); ranked at the 3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — 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-2026-21916 is a UNIX Symbolic Link (Symlink) Following vulnerability (CWE-61) in the CLI of Juniper Networks Junos OS, with a CVSS v3.1 base score of 7.3 (AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H). It affects Junos OS all versions before 23.2R2-S7, 23.4 versions before 23.4R2-S6, 24.2 versions before 24.2R2-S3, 24.4 versions before 24.4R2-S2, and 25.2 versions before 25.2R2. Versions 25.4R1 and later are not affected.
A local, authenticated attacker with low privileges can exploit this vulnerability to escalate privileges to root, resulting in complete system compromise. The attack scenario requires one user to perform a specific 'file link ...' CLI operation, after which another user commits unrelated configuration changes; the first user can then log in as root.
The Juniper security advisory at https://kb.juniper.net/JSA107807 details mitigation, which involves upgrading to a supported, patched release of Junos OS as specified in the affected versions.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-21080
Vulnerability Data
A UNIX Symbolic Link (Symlink) Following vulnerability in the CLI of Juniper Networks Junos OS allows a local, authenticated attacker with low privileges to escalate their privileges to root which will lead to a complete compromise of the system. When…
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after a user has performed a specific 'file link ...' CLI operation, another user commits (unrelated configuration changes), the first user can login as root. This issue affects Junos OS: * all versions before 23.2R2-S7, * 23.4 versions before 23.4R2-S6, * 24.2 versions before 24.2R2-S3, * 24.4 versions before 24.4R2-S2, * 25.2 versions before 25.2R2. This issue does not affect versions 25.4R1 or later.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 2 hardening rules · 2 OS baselines
V5.2.5
Mitigating Controls (NIST 800-53 r5) AI
Access enforcement must resolve the actual target of any file reference and apply authorizations to it, directly stopping symlink traversal to unauthorized objects.
Information-flow enforcement on file operations must follow the resolved target rather than the link name, blocking unauthorized data movement via symlinks.
Least-privilege restrictions on the directories that may contain links or targets reduce the set of files an attacker can reach even if a symlink is followed.
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.
Secure SDLC practices directly prevent introduction of symlink-following flaws in file-handling code.
Vulnerability identification can discover existing symlink issues but does not prevent or remediate them in code.
Least-privilege access policies can limit damage from symlink attacks but do not address the coding flaw itself.
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 can detect symlink-following vulnerabilities before deployment, covering most of the weakness.
Secure-architecture principles require safe file-handling and canonicalization, directly addressing symlink attacks.
Secure-coding standards mandate explicit symlink checks and safe open patterns, fully mitigating CWE-61.
Access-control rules can restrict which files a process may open, reducing symlink-following risk but not eliminating the underlying path-resolution flaw.
Configuration management can enforce safe file-permission baselines that limit symlink abuse, but does not address the code flaw itself.
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-61