An Improper Validation of Syntactic Correctness of Input vulnerability in the Web-Filtering module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). This vulnerability is particularly critical as it affects network devices that are integral to organizational security.
If an SRX device configured for UTM Web-Filtering receives a specifically malformed SSL packet, this will cause an FPC crash and restart. The affected versions include Junos OS 23.2 from 23.2R2-S2 before 23.2R2-S5, 23.4 from 23.4R2-S1 before 23.4R2-S5, 24.2 before 24.2R2-S2, and 24.4 before 24.4R1-S3, 24.4R2. Organizations running these versions must act promptly.
This vulnerability has been scored with a CVSS base score of 8.7, reflecting its high severity. Risk to organizations includes potential downtime, which can disrupt critical services and lead to significant operational impacts.
Given the exploitability and the nature of the vulnerability, organizations should prioritize patching immediately to mitigate the risk of a Denial-of-Service attack.
Vulnerability Details
The vulnerability allows attackers to exploit the Web-Filtering module within Junos OS. The CVSS score of 8.7 indicates a high severity with an availability impact categorized as high. The affected products include various versions of Junos OS on SRX Series devices.
The vulnerability was published on January 15, 2026, and is classified under CWE-1286. It is crucial for organizations to assess their current versions and apply necessary patches provided by Juniper.
Technical Analysis
The root cause of this vulnerability stems from improper validation of SSL packets. The attack vector is network-based, and the attack complexity is rated as low, meaning that an attacker does not require special conditions to exploit it. No user interaction is necessary, allowing for remote attacks without prior access.
In terms of impact, the vulnerability has a high availability impact due to the potential for Denial-of-Service conditions. Organizations should evaluate their configurations to ensure they are not vulnerable to this threat.
Risk & Impact Analysis
The real-world risk associated with this vulnerability includes the possibility of downtime for critical services, which can severely affect business operations. The urgency for organizations to address this vulnerability is high, given the CVSS score and the nature of the vulnerability itself.
The blast radius is significant, as the vulnerability affects multiple versions of Junos OS across various SRX Series devices, which are commonly deployed in enterprise environments. Organizations should assess their exposure and act accordingly.
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
This vulnerability affects the following versions of Junos OS on SRX Series devices: 23.2 from 23.2R2-S2 before 23.2R2-S5, 23.4 from 23.4R2-S1 before 23.4R2-S5, 24.2 before 24.2R2-S2, and 24.4 before 24.4R1-S3, 24.4R2. All versions prior to vendor patch are also affected.
Mitigation & Remediation
Organizations should apply patches to the affected Junos OS versions as soon as they are available. If patches are not yet available, consider implementing workarounds such as filtering malformed packets at the network level, enhancing monitoring for unusual traffic patterns, and conducting regular security assessments to identify vulnerabilities.
Organizations should also consider leveraging penetration testing to validate the effectiveness of their security measures.
Detection Guidance
Monitor logs for unusual patterns, especially related to SSL packet processing. Look for signs of FPC crashes or restarts, which may indicate attempts to exploit this vulnerability. Network signatures for malformed SSL packets should be developed and deployed.
AppSecure Threat Intelligence Insight
This vulnerability highlights the ongoing challenges faced by network security teams in maintaining the integrity and availability of critical infrastructure. As attackers continuously seek to exploit such weaknesses, organizations must remain vigilant and proactive in their security posture.
By understanding the attack vectors and potential impacts of vulnerabilities like CVE-2026-21917, security teams can prioritize their defenses effectively. Organizations should consider adopting a comprehensive security framework that includes vulnerability management programs to ensure timely identification and remediation of security issues.
Additionally, regular security assessments, including penetration testing methodologies, can provide valuable insights into potential vulnerabilities before they can be exploited.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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