Junos OS (SRX firewalls)
CVE-2026-21917: SRX Series: Specifically malformed SSL packet causes FPC crash
An Improper Validation of Syntactic Correctness of Input vulnerability in the Web-Filtering module 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) 23.2R2-S2 | 23.2R2-S5 or later |
| Junos OS (SRX Series) 23.4R2-S1 | 23.4R2-S5 or later |
| Junos OS (SRX Series) 24.2 | 24.2R2-S2 or later |
| Junos OS (SRX Series) 24.4 | 24.4R1-S3, 24.4R2 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 the Web-Filtering module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).
If an SRX device configured for UTM Web-Filtering receives a specifically malformed SSL packet, this will cause an FPC crash and restart. This issue affects Junos OS on SRX Series:
- 23.2 versions from 23.2R2-S2 before 23.2R2-S5,
- 23.4 versions from 23.4R2-S1 before 23.4R2-S5,
- 24.2 versions before 24.2R2-S2,
- 24.4 versions before 24.4R1-S3, 24.4R2.
Earlier versions of Junos are also affected, but no fix is available.
Am I affected?
To be exposed to this issue web-filtering needs to be configured as follows:
[ security utm utm-policy <utm policy name> web-filtering http-profile <name> ] [ security policies ... policy <security policy name> then permit application-services utm-policy <utm policy name> ]
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.