Junos OS (SRX firewalls)
CVE-2024-21601: SRX Series: Due to an error in processing TCP events flowd will crash
A Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') vulnerability in the Flow-processing Daemon (flowd) of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a 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 (SRX Series) 21.2 | 21.2R3-S5 or later |
| Junos OS (SRX Series) 21.3 | 21.3R3-S5 or later |
| Junos OS (SRX Series) 21.4 | 21.4R3-S4 or later |
| Junos OS (SRX Series) 22.1 | 22.1R3-S3 or later |
| Junos OS (SRX Series) 22.2 | 22.2R3-S1 or later |
| Junos OS (SRX Series) 22.3 | 22.3R2-S2, 22.3R3 or later |
| Junos OS (SRX Series) 22.4 | 22.4R2-S1, 22.4R3 or later |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
A Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') vulnerability in the Flow-processing Daemon (flowd) of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (Dos).
On SRX Series devices when two different threads try to simultaneously process a queue which is used for TCP events flowd will crash. One of these threads can not be triggered externally, so the exploitation of this race condition is outside the attackers direct control.
Continued exploitation of this issue will lead to a sustained DoS.
This issue affects Juniper Networks Junos OS:
- 21.2 versions earlier than 21.2R3-S5;
- 21.3 versions earlier than 21.3R3-S5;
- 21.4 versions earlier than 21.4R3-S4;
- 22.1 versions earlier than 22.1R3-S3;
- 22.2 versions earlier than 22.2R3-S1;
- 22.3 versions earlier than 22.3R2-S2, 22.3R3;
- 22.4 versions earlier than 22.4R2-S1, 22.4R3.
This issue does not affect Juniper Networks Junos OS versions earlier than 21.2R1.
Workarounds
There are no known workarounds for this issue.
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.