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Actively exploited

CVE-2015-7755 Juniper ScreenOS Improper Authentication Vulnerability

Juniper ScreenOS contains an improper authentication vulnerability that could allow unauthorized remote administrative access to the device.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 2 Oct 2025.
  • Rated Critical severity (CVSS 9.8, scored by CISA).
  • It has been in the catalogue for 400 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

Juniper ScreenOS 6.2.0r15 through 6.2.0r18, 6.3.0r12 before 6.3.0r12b, 6.3.0r13 before 6.3.0r13b, 6.3.0r14 before 6.3.0r14b, 6.3.0r15 before 6.3.0r15b, 6.3.0r16 before 6.3.0r16b, 6.3.0r17 before 6.3.0r17b, 6.3.0r18 before 6.3.0r18b, 6.3.0r19 before 6.3.0r19b, and 6.3.0r20 before 6.3.0r21 allows remote attackers to obtain administrative access by entering an unspecified password during a (1) SSH or (2) TELNET session.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Juniper ScreenOS. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 23 Oct 2025 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited Juniper Flaws

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CVE-2025-21590Juniper Junos OS Improper Isolation or Compartmentalization VulnerabilityAdded 13 Mar 2025CVE-2023-36844Juniper Junos OS EX Series PHP External Variable Modification VulnerabilityAdded 13 Nov 2023CVE-2023-36845Juniper Junos OS EX Series and SRX Series PHP External Variable Modification VulnerabilityAdded 13 Nov 2023CVE-2023-36846Juniper Junos OS SRX Series Missing Authentication for Critical Function VulnerabilityAdded 13 Nov 2023CVE-2023-36847Juniper Junos OS EX Series Missing Authentication for Critical Function VulnerabilityAdded 13 Nov 2023CVE-2023-36851Juniper Junos OS SRX Series Missing Authentication for Critical Function VulnerabilityAdded 13 Nov 2023

All 8 exploited Juniper vulnerabilities

Not Sure If You Are Exposed?

Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2015-7755 and every other exploited flaw on the list.

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2015-7755
  3. CVE record: CVE-2015-7755
  4. FIRST EPSS
  5. supportportal.juniper.net/s/article/2015-12-Out-of-Cycle-Security-Bulletin-ScreenOS-Multiple-Securit
  6. arstechnica.com/security/2015/12/unauthorized-code-in-juniper-firewalls-decrypts-encrypted-vpn-traff
  7. wired.com/2015/12/juniper-networks-hidden-backdoors-show-the-risk-of-government-backdoors/
  8. securitytracker.com/id/1034489
  9. kb.cert.org/vuls/id/640184
  10. forums.juniper.net/t5/Security-Incident-Response/Important-Announcement-about-ScreenOS/ba-p/285554
  11. github.com/hdm/juniper-cve-2015-7755
  12. kb.juniper.net/InfoCenter/index?page=content&id=JSA10713