CVE-2024-21606: SRX Series: When "tcp-encap" is configured and specific packets are received flowd will crash

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) 0	20.4R3-S8 or later
Junos OS (SRX Series) 21.2	21.2R3-S6 or later
Junos OS (SRX Series) 21.3	21.3R3-S5 or later
Junos OS (SRX Series) 21.4	21.4R3-S5 or later
Junos OS (SRX Series) 22.1	22.1R3-S3 or later
Junos OS (SRX Series) 22.2	22.2R3-S3 or later
Junos OS (SRX Series) 22.3	22.3R3-S1 or later
Junos OS (SRX Series) 22.4	22.4R2-S2, 22.4R3 or later

Always confirm against the vendor advisory, which lists every fixed hotfix.

What it is

A Double Free vulnerability in the flow processing daemon (flowd) of Juniper Networks Junos OS on SRX Series allows a network-based, unauthenticated attacker to cause a Denial of Service (DoS).

In a remote access VPN scenario, if a "tcp-encap-profile" is configured and a sequence of specific packets is received, a flowd crash and restart will be observed.

This issue affects Juniper Networks Junos OS on SRX Series:

All versions earlier than 20.4R3-S8;
21.2 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-S3;
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.

Am I affected?

To be exposed to this issue the following configuration needs to be present:

[security ike gateway <gateway-name> tcp-encap-profile <profile-name> ]

Workarounds

There are no known workarounds for this issue.

Exploitation

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

KEV status, EPSS score and vendor data refreshed automatically, last on 13 Oct 2026.