Security readout for executives and security teams
Plain-English summary
This Junos OS issue lets a logged-in user with shell access read sensitive local files through a root-owned mosquitto SUID binary. It is not described as remote code execution, but it can expose high-value device secrets, including password file content.
Executive priority
Treat as a moderate, targeted infrastructure risk. It does not appear remotely exploitable from the provided evidence, but affected network devices can expose sensitive local secrets after a user gains shell access.
Technical view
CVE-2021-0256 is a CWE-250 privilege-management flaw in Junos OS mosquitto packaging. Because mosquitto is root-owned and setuid, a low-privileged local shell user may access sensitive filesystem data. CVSS 3.1 is 5.5: local attack, low complexity, low privileges, no user interaction, high confidentiality impact.
Likely exposure
Exposure is limited to Juniper Networks Junos OS 17.3, 17.4, 18.1, 18.3, 19.1, 19.3, 19.4, 20.1, and 20.2 before the fixed releases listed by Juniper.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. Exploitation requires local authenticated shell access, so risk is highest where many users can access device shells or credentials are already compromised.
Researcher notes
Key constraints are local access, low privileges, no user interaction, and confidentiality-only impact in CVSS. Validate SUID mosquitto exposure only within authorized environments and avoid assuming broader products or exploit availability beyond Juniper’s affected Junos OS ranges.
Mitigation direction
- Upgrade affected Junos OS devices to the fixed release for their train or later.
- Review Juniper advisory JSA11175 for platform-specific upgrade guidance.
- Restrict local shell access to trusted administrators until upgrades are complete.
- Prioritize internet-edge and high-privilege network devices for remediation.
- Monitor affected devices for unusual local sensitive-file access.
Validation and detection
- Inventory Junos OS versions across routers, switches, and security appliances.
- Compare each device version against the affected release ranges listed by Juniper.
- Confirm whether local shell access is enabled and who can use it.
- Verify remediated devices run a fixed or later Junos OS release.
- Check vulnerability scanner results against Juniper advisory JSA11175.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-250: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupPrivilege behavior lookup
The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-0256 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://kb.juniper.net/JSA11175CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Execution with Unnecessary Privileges
Execution with Unnecessary Privileges represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.