SB2026012061 - Infinite loop in Juniper Junos OS

Security Bulletin ID SB2026012061

Severity

Medium

Patch available

YES

Number of vulnerabilities 1

Exploitation vector Remote access

Highest impact Denial of service

Breakdown by Severity

Low
Medium
High
Critical

Description

This security bulletin contains information about 1 security vulnerability.

1) Infinite loop (CVE-ID: CVE-2026-21905)

The vulnerability allows a remote non-authenticated attacker to perform a denial of service (DoS) attack.

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.

Remediation

Install update from vendor's website.

References

https://supportportal.juniper.net/s/article/2026-01-Security-Bulletin-Junos-OS-SRX-Series-MX-Series-with-MX-SPC3-or-MS-MPC-Receipt-of-multiple-specific-SIP-messages-results-in-flow-management-process-crash-CVE-2026-21905