CVE-2021-1534 Cisco Email Security Appliance URL Filtering Bypass Vulnerability
An unauthenticated remote attacker can bypass URL reputation filters on Cisco Email Security Appliances by crafting specific URLs, allowing malicious links to pass through.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2021-1534?
CVE-2021-1534 is a medium-severity vulnerability in Cisco Asyncos, published on 6 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A vulnerability in the antispam protection mechanisms of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to bypass the URL reputation filters on an affected device. This vulnerability is due to improper processing of URLs. An attacker could exploit this vulnerability by crafting a URL in a particular way. A successful exploit could allow the attacker to bypass the URL reputation filters that are configured for an affected device, which could allow malicious URLs to pass through the device.
Weakness: CWE-20
Which versions are affected by CVE-2021-1534?
It affects 1 product.
Products include Cisco Asyncos.
How do I fix CVE-2021-1534?
No fix has been published for CVE-2021-1534 yet. Limit exposure of the affected software until one is available.
Is CVE-2021-1534 being exploited?
There is no known exploitation of CVE-2021-1534 in the wild and no public exploit code.
Other vulnerabilities in Cisco Asyncos
- CVE-2025-20393 Cisco Multiple Products Improper Input Validation
- CVE-2026-76519 Cisco Secure Email Gateway Relative Path Traversal
- CVE-2026-76461 Cisco Secure Email Gateway SQL Injection
- CVE-2024-20435 Command injection in Cisco Secure Web Appliance
- CVE-2019-15956 Cisco Web Security Appliance Unauthorized Device Reset Vulnerability
Sources
Also known as GHSA-86vv-w52w-qq85.