Security readout for executives and security teams
Plain-English summary
This Junos OS flaw can let an unauthenticated network attacker knock out web-based Juniper services for an extended period. It affects J-Web and several HTTP/HTTPS-backed access or authentication features. It does not indicate data theft or device takeover, but it can disrupt administration, VPN access, captive portal, and web authentication workflows.
Executive priority
Prioritize remediation where Juniper web services support administration, VPN access, or user authentication. Business risk is service disruption, not confirmed compromise. Internet-reachable management or access portals should be handled first.
Technical view
CVE-2021-0261 is a network-reachable availability vulnerability in Junos OS HTTP/HTTPS services. A high number of specific requests can trigger extended denial of service in J-Web, Web Authentication, DVPN, Firewall Authentication Pass-Through with Web-Redirect, and Captive Portal. CVSS 3.1 is 7.5: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
Likely exposure
Exposure is most relevant where affected Junos OS EX or SRX devices run J-Web or listed HTTP/HTTPS-backed services, especially if reachable from untrusted networks. The source bundle does not identify affected configurations beyond those services and release trains.
Exploitation context
The CVE describes unauthenticated network exploitation for denial of service. The source bundle does not show CISA KEV listing or cite public active exploitation. Treat exploitation as plausible from reachable networks, but do not assume observed exploitation without local evidence.
Researcher notes
The advisory maps to CWE-125 and CWE-770, suggesting malformed handling or resource exhaustion behavior. Available evidence supports DoS impact only. Avoid assuming broader control-plane compromise, persistence, or data exposure unless separate evidence is found.
Mitigation direction
- Upgrade affected devices to the fixed Junos OS releases or later listed by Juniper.
- Prioritize internet-facing or partner-reachable J-Web, DVPN, web authentication, and captive portal deployments.
- Check Juniper JSA11152 for vendor-approved workarounds or compensating controls.
- Plan maintenance carefully because remediation may require network device software upgrades.
Validation and detection
- Inventory Junos OS versions on EX and SRX devices.
- Confirm whether J-Web or listed HTTP/HTTPS-backed services are enabled.
- Compare device versions against Juniper’s affected and fixed release thresholds.
- Review monitoring for repeated outages of J-Web, DVPN, or captive portal services.
- Confirm upgraded systems report a fixed release or later.
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-125: 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 lookupCWE-770: 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 lookupCVE-2021-0261 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
- High
- CVSS
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://kb.juniper.net/JSA11152CVE 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.
Out-of-bounds Read
Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Allocation of Resources Without Limits or Throttling
Allocation of Resources Without Limits or Throttling represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.