CVE-2020-1999: PAN-OS: Threat signatures are evaded by specifically crafted packets

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2020-11-12 · updated 2026-06-17
Weakness: CWE-754

Description

A vulnerability exists in the Palo Alto Network PAN-OS signature-based threat detection engine that allows an attacker to communicate with devices in the network in a way that is not analyzed for threats by sending data through specifically crafted TCP packets. This technique evades signature-based threat detection. This issue impacts: PAN-OS 8.1 versions earlier than 8.1.17; PAN-OS 9.0 versions earlier than 9.0.11; PAN-OS 9.1 versions earlier than 9.1.5; All versions of PAN-OS 7.1 and PAN-OS 8.0.

Affected products

Palo Alto Networks PAN-OS: from 7.1.0 through 7.1.26; from 8.0.0 through 8.0.20; from 8.1.0 before 8.1.17; from 9.0.0 before 9.0.11; from 9.1.0 before 9.1.5 — fixed in 8.1.17, 9.0.11, 9.1.5
Palo Alto Networks PAN-OS: from 8.1 before 8.1.17; from 9.0 before 9.0.11; from 9.1 before 9.1.5; 7.1.*, 8.0.* — fixed in 8.1.17, 9.0.11, 9.1.5

How to fix

Upgrade to a fixed version: Palo Alto Networks PAN-OS 8.1.17, 9.0.11, 9.1.5; Palo Alto Networks PAN-OS 8.1.17, 9.0.11, 9.1.5. Check the vendor advisory for mitigations.

References

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