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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 23 Oct 2025.
ScreenosOperating system · Juniper

CVE-2015-7755

CRITICAL · 9.8 CVSS v3.1 Published 2015-12-19
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Juniper ScreenOS contains a hardcoded backdoor password that grants administrative access when entered during SSH or TELNET authentication. Attackers can obtain full administrative control of affected firewall and VPN devices without knowing the legitimate credentials, by using this undisclosed password.

MitigationApply Juniper patches (6.2.0r19+, 6.3.0r21+) to remove the backdoor. Until patched, restrict SSH/TELNET management access to trusted management networks only using firewall rules or jump hosts, and monitor for unauthorized administrative sessions.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
ScreenosOperating system
Affected:= 6.3.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify ScreenOS version
    Run 'get system information' or 'show version' command on the Juniper device to retrieve the installed ScreenOS version and build number
    Affected if Version is 6.2.0r15 through 6.2.0r18, or 6.3.0r12 through 6.3.0r20 (including 6.3.0) - compare your exact version string to these ranges
  2. Verify if SSH access is enabled
    Run 'get system ssh status' or check the configuration with 'show configuration' looking for 'set system ssh' statements
    Affected if SSH is enabled on the device (the backdoor can be exploited via SSH)
  3. Verify if TELNET access is enabled
    Run 'get system telnet status' or check the configuration for 'set system telnet' statements
    Affected if TELNET is enabled on the device (the backdoor can be exploited via TELNET)
  4. Review admin login logs for suspicious activity
    Run 'get log system' and search for administrative login events, especially from unknown IPs or at unusual times, or check for multiple failed authentication attempts followed by successful logins
    Affected if Log entries show administrative logins that cannot be attributed to legitimate administrators, or show the undocumented backdoor password being used

Your device is affected if it runs ScreenOS version 6.2.0r15-r18 or 6.3.0r12-r20 (or 6.3.0) and has SSH or TELNET access enabled, allowing the hardcoded backdoor password to be used for unauthorized admin access.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Juniper patches (6.2.0r19+, 6.3.0r21+) to remove the backdoor. Until patched, restrict SSH/TELNET management access to trusted management networks only using firewall rules or jump hosts, and monitor for unauthorized administrative sessions.

Recommended fix High confidence

Screenos 6.3.0r21 (or respective 'b' patch for earlier versions: r12b, r13b, r14b, r15b, r16b, r17b, r18b, r19b)

  1. 1. Identify the current ScreenOS version by running 'get system' or 'show version' command on the device
  2. 2. Determine which patch level applies to your current version (e.g., if on 6.3.0r20, you need 6.3.0r21)
  3. 3. Download the appropriate patched release from the Juniper Netscreen ScreenOS downloads page or Juniper support portal
  4. 4. Upload the new ScreenOS image to the device using 'save software' or through the web UI (Device > Update > ScreenOS)
  5. 5. Reboot the device to load the new ScreenOS version using 'reboot' command
  6. 6. After reboot, verify the new version is running with 'get system' or 'show version'
  7. 7. Change all administrative passwords immediately after applying the patch, as a precaution
  8. 8. Review admin accounts and SSH/TELNET access configurations to ensure no unauthorized accounts exist
Caveat ScreenOS is End-of-Life (EOL); consider migrating to Junos OS asScreenOS is no longer supported

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Screenos Exploited in the wild — priority engagement
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
36.0 hours of engineering $6,400
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2015-7755 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
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  • Version or environment caveats, and links to real fixes
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