Junos OS: UNIX Symbolic Link (Symlink) Following
CVE-2026-21916 is a high-severity UNIX symbolic link (symlink) following vulnerability in Junos OS from Juniper Networks, with a CVSS 3.1 base score of 7.3 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, but only if a user takes part, for example by opening a link or file. The record lists versions 23.2R2-S7, 23.4R2-S6, 24.2R2-S3 as the first without the flaw, so updating Junos OS to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.13% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Junos OS to 23.2R2-S7 or 23.4R2-S6 or 24.2R2-S3 or 24.4R2-S2, whichever matches your release line, or a later version.
- Update Junos to 23.2 or a later version.
- Read the advisory on kb.juniper.net for workarounds and exact fixed builds.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Juniper Networks | Junos OS | before 23.2R2-S7; 23.4 up to, but not including, 23.4R2-S6; 24.2 up to, but not including, 24.2R2-S3; 24.4 up to, but not including, 24.4R2-S2; 25.2 up to, but not including, 25.2R2 | 23.2R2-S7, 23.4R2-S6, 24.2R2-S3, 24.4R2-S2, 25.2R2 |
| Juniper Networks | Junos | before 23.2; 23.2; 23.4; 24.2; 24.4; 25.2 | 23.2 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H. Scored by CNA (juniper.net).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 7.0 | High | CNA (juniper.net) |
| CVSS 3.1 | 7.3 | High | CNA (juniper.net) |
Official description
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 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: UNIX Symbolic Link (Symlink) Following
The product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files.
How developers prevent this class of flaw
- Symbolic link attacks often occur when a program creates a tmp directory that stores files/links. Access to the directory should be restricted to the program as to prevent attackers from manipulating the files.
- Follow the principle of least privilege when assigning access rights to entities in a software system. Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.
More UNIX Symbolic Link (Symlink) Following vulnerabilities (CWE-61)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- kb.juniper.net/JSA107807Mitigation
Other vulnerabilities in Junos OS
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 8.8 High severity
- 8.8 High severity
- 7.5 High severity
Recent UNIX Symbolic Link (Symlink) Following vulnerabilities
- 7.8 High severity
- 8.4 High severity
- 7.5 High severity
- 10.0 Critical severity
- 7.3 High severity
- 7.8 High severity
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