Juniper Junos OS SRX/MX SIP ALG TCP Infinite Loop DoS <25.2R2
CVE-2026-21905 Published on January 15, 2026
Junos OS: SRX Series, MX Series with MX-SPC3 or MS-MPC: Receipt of multiple specific SIP messages results in flow management process crash
A Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in the SIP application layer gateway (ALG) of Juniper Networks Junos OS on SRX Series and MX Series with MX-SPC3 or MS-MPC allows an unauthenticated network-based attacker sending specific SIP messages over TCP to crash the flow management process, leading to a Denial of Service (DoS).
On SRX Series, and MX Series with MX-SPC3 or MS-MPC service cards, receipt of multiple SIP messages causes the SIP headers to be parsed incorrectly, eventually causing a continuous loop and leading to a watchdog timer expiration, crashing the flowd process on SRX Series and MX Series with MX-SPC3, or mspmand process on MX Series with MS-MPC.
This issue only occurs over TCP. SIP messages sent over UDP cannot trigger this issue.
This issue affects Junos OS on SRX Series and MX Series with MX-SPC3 and MS-MPC:
* all versions before 21.2R3-S10,
* from 21.4 before 21.4R3-S12,
* from 22.4 before 22.4R3-S8,
* from 23.2 before 23.2R2-S5,
* from 23.4 before 23.4R2-S6,
* from 24.2 before 24.2R2-S3,
* from 24.4 before 24.4R2-S1,
* from 25.2 before 25.2R1-S1, 25.2R2.
Vulnerability Analysis
CVE-2026-21905 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is an Infinite Loop Vulnerability?
The program contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. If the loop can be influenced by an attacker, this weakness could allow attackers to consume excessive resources such as CPU or memory.
CVE-2026-21905 has been classified to as an Infinite Loop vulnerability or weakness.
Products Associated with CVE-2026-21905
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Affected Versions
Juniper Networks Junos OS:- Before 21.2R3-S10 is affected.
- Version 21.4 and below 21.4R3-S12 is affected.
- Version 22.4 and below 22.4R3-S8 is affected.
- Version 23.2 and below 23.2R2-S5 is affected.
- Version 23.4 and below 23.4R2-S6 is affected.
- Version 24.2 and below 24.2R2-S3 is affected.
- Version 24.4 and below 24.4R2-S1 is affected.
- Version 25.2 and below 25.2R1-S1, 25.2R2 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.