Juniper ScreenOS Remote Administrative Access Backdoor Vulnerability (CVE-2015-7755) Analysis and Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTJuniper ScreenOS versions 6.2.0r15 through 6.2.0r18 and 6.3.0r12 through 6.3.0r20
Remote attackers can bypass authentication and gain full administrative (root) access to the firewall via SSH or TELNET using a hardcoded master password
Immediately upgrade ScreenOS to patched versions (6.3.0r21 or the respective 'b' releases) and disable external SSH/TELNET access
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
The primary remediation is to upgrade the ScreenOS firmware to a patched release (6.3.0r21 or the specific 'b' release for your current branch).
# Load and upgrade the secure ScreenOS image from a TFTP server
save software from tftp 192.168.1.100 ns500.6.3.0r21 to flash
# Reboot the firewall to apply the new firmware
reset2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, disable administrative access on untrusted interfaces and restrict management access to trusted IP addresses only.
# Disable SSH and TELNET management on the external/untrusted interface
set interface ethernet1/1 manage no-ssh
set interface ethernet1/1 manage no-telnet
# Restrict administrative access to a trusted management subnet
set admin auth ip 10.10.10.0 255.255.255.03. Log Audit & IoC Verification Commands
Verify the running ScreenOS version and inspect system logs for unauthorized administrative access attempts.
# Check the current ScreenOS version
get system
# Audit system logs for admin login events and suspicious source IPs
get db stream | include 'auth'
get event | include 'admin'Stop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2015-7755) stems from unauthorized backdoor code inserted into the source code of Juniper's ScreenOS operating system. The root cause lies within the authentication module (CWE-287), where a specific master password was hardcoded, allowing any login attempt with a valid username to bypass standard password verification and grant administrative privileges.
2. Exploitation Mechanics & Attack Scenario
An attacker scans for target devices with SSH (port 22) or TELNET (port 23) services exposed to the internet. By initiating a session, entering a valid username (such as 'admin'), and providing the hardcoded backdoor password, the internal authentication logic of ScreenOS evaluates the credential as valid. This bypasses normal authentication mechanisms and drops the attacker directly into an administrative shell.
3. Infrastructure & Business Impact
With a CVSS score of 9.8 (Critical) and its inclusion in the CISA KEV catalog, this vulnerability poses an extreme risk. Successful exploitation grants complete control over the firewall. Attackers can intercept or decrypt VPN traffic, alter security policies, and pivot into the internal corporate network, leading to catastrophic data breaches and total infrastructure compromise.
Official Vendor Advisories & References
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.
Frequently Asked SecOps Questions (CVE-2015-7755)
FAQQ1. How critical is CVE-2015-7755 and is it actively exploited in the wild?
CVE-2015-7755 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 61.1%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2015-7755?
Primary impacted vendors include juniper across screenos. Scope summary: Juniper ScreenOS 6.2.0r15 through 6.2.0r18, and 6.3.0r12 through 6.3.0r20 (prior to 6.3.0r12b through r20b, or 6.3.0r21)
Q3. What temporary mitigations or workarounds exist for CVE-2015-7755 before patching?
[Mitigation] Immediately upgrade ScreenOS to patched versions (6.3.0r21 or the respective 'b' releases) and disable external SSH/TELNET access Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2015-7755
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