Junos OS Evolved: Incorrect Permission Assignment for Critical Resource
CVE-2026-21902 is a critical-severity incorrect permission assignment for critical resource vulnerability in Junos OS Evolved from Juniper Networks, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 25.4R1-S1-EVO, 25.4R2-EVO as the first without the flaw, so updating Junos OS Evolved to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 18.5% chance of exploitation within 30 days, which is in the top 2.71% of all scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Junos OS Evolved to 25.4R1-S1-EVO, 25.4R2-EVO or a later version.
- Read the advisory on kb.juniper.net for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Juniper Networks | Junos OS Evolved | 25.4 up to, but not including, 25.4R1-S1-EVO, 25.4R2-EVO | 25.4R1-S1-EVO, 25.4R2-EVO |
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
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- 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:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (juniper.net).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.3 | Critical | CNA (juniper.net) |
| CVSS 3.1 | 9.8 | Critical | CNA (juniper.net) |
Official description
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 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Incorrect Permission Assignment for Critical Resource
The product specifies permissions for a security-critical resource in a way that allows that resource to be read or modified by unintended actors.
How developers prevent this class of flaw
- When using a critical resource such as a configuration file, check to see if the resource has insecure permissions (such as being modifiable by any regular user), and generate an error or even exit the software if there is a possibility that the resource could have been modified by an unauthorized party.
- Divide the software into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully defining distinct user groups, privileges, and/or roles. Map these against data, functionality, and the related resources. Then set the permissions accordingly. This will allow you to maintain more fine-grained control over your resources.
- During program startup, explicitly set the default permissions or umask to the most restrictive setting possible. Also set the appropriate permissions during program installation. This will prevent you from inheriting insecure permissions from any user who installs or runs the program.
More Incorrect Permission Assignment for Critical Resource vulnerabilities (CWE-732)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- kb.juniper.net/JSA107128Mitigation
- supportportal.juniper.net/JSA107128Mitigation
Other references
Other vulnerabilities in Junos OS Evolved
- 9.8 Critical severity
- 9.8 Critical severity
- 8.8 High severity
- 8.8 High severity
- 7.5 High severity
- 7.5 High severity
Recent Incorrect Permission Assignment for Critical Resource vulnerabilities
- 8.8 High severity
- 7.4 High severity
- 7.8 High severity
- 7.0 High severity
- 7.5 High severity
- 10.0 Critical severity
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