High [CVE-2026-21905] Junos: Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in the SIP application layer gateway (ALG) of Juniper…
This high-severity Juniper Networks advisory covers CVE-2026-21905 affecting Junos, Junos OS, SRX.
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Summary
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.
- all versions before 21.2R3-S10,
- from 21.4 before 21.4R3-S12,
- from 23.2 before 23.2R2-S5,
- from 23.4 before 23.4R2-S6,
Affected products named by the advisory: MX; EX.
- 21.4
- 22.4
- 23.2
- 23.4
- 24.2
- 24.4
- 25.2
- all versions
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
- 21.2R3-S10
- 21.4R3-S12
- 22.4R3-S8
- 23.2R2-S5
- 23.4R2-S6
- 24.2R2-S3
- 24.4R2-S1
- 25.2R1-S1
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation
Upgrade to a fixed release: 21.2R3-S10, 21.4R3-S12, 22.4R3-S8, 23.2R2-S5, 23.4R2-S6, 24.2R2-S3. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
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