Junos OS (SRX firewalls)
CVE-2024-21616: MX Series and SRX Series: Processing of a specific SIP packet causes NAT IP allocation to fail
An Improper Validation of Syntactic Correctness of Input vulnerability in Packet Forwarding Engine (PFE) of Juniper Networks Junos OS allows an unauthenticated, network-based attacker to cause Denial of Service (DoS).
Published
Automatic summary from the vendor's CVE record. We haven't written a full analysis of this vulnerability yet.
Affected and fixed versions
| Product / branch | Fixed in |
|---|---|
| Junos OS (MX Series, SRX Series) 0 | 21.2R3-S6 or later |
| Junos OS (MX Series, SRX Series) 21.3 | 21.3R3-S5 or later |
| Junos OS (MX Series, SRX Series) 21.4 | 21.4R3-S5 or later |
| Junos OS (MX Series, SRX Series) 22.1 | 22.1R3-S4 or later |
| Junos OS (MX Series, SRX Series) 22.2 | 22.2R3-S3 or later |
| Junos OS (MX Series, SRX Series) 22.3 | 22.3R3-S1 or later |
| Junos OS (MX Series, SRX Series) 22.4 | 22.4R2-S2, 22.4R3 or later |
| Junos OS (MX Series, SRX Series) 23.2 | 23.2R1-S1, 23.2R2 or later |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
An Improper Validation of Syntactic Correctness of Input vulnerability in Packet Forwarding Engine (PFE) of Juniper Networks Junos OS allows an unauthenticated, network-based attacker to cause Denial of Service (DoS).
On all Junos OS MX Series and SRX Series platforms, when SIP ALG is enabled, and a specific SIP packet is received and processed, NAT IP allocation fails for genuine traffic, which causes Denial of Service (DoS). Continuous receipt of this specific SIP ALG packet will cause a sustained DoS condition.
NAT IP usage can be monitored by running the following command.
user@srx> show security nat resource-usage source-pool <source_pool_name>
Pool name: source_pool_name .. Address Factor-index Port-range Used Avail Total Usage X.X.X.X 0 Single Ports 50258 52342 62464 96% <<<<< - Alg Ports 0 2048 2048 0% This issue affects:
Juniper Networks Junos OS on MX Series and SRX Series
- All versions earlier than 21.2R3-S6;
- 21.3 versions earlier than 21.3R3-S5;
- 21.4 versions earlier than 21.4R3-S5;
- 22.1 versions earlier than 22.1R3-S4;
- 22.2 versions earlier than 22.2R3-S3;
- 22.3 versions earlier than 22.3R3-S1;
- 22.4 versions earlier than 22.4R2-S2, 22.4R3;
- 23.2 versions earlier than 23.2R1-S1, 23.2R2.
Am I affected?
To be affected the SIP ALG needs to be enabled, either implicitly / by default or by way of configuration.
Please verify on SRX with:
user@host> show security alg status | match sip SIP : Enabled Please verify on MX whether the following is configured:
user@host> show security alg status | match sip SIP : Enabled [services ... rule <rule-name> (term <term-name> ) from/match application/application-set <name>] where either
a. name = junos-sip or an application or application-set refers to SIP:
b. [applications application <name> application-protocol sip] or
c. [applications application-set <name> application junos-sip]
Workarounds
There are no known workarounds for this issue, but it should be considered to disable the SIP ALG if it's not strictly needed.
Exploitation
Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
Sources
KEV status, EPSS score and vendor data refreshed automatically, last on 13 Oct 2026.