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Fencer Vulns
medium 4.7

CVE-2020-3561 json

Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software WebVPN CRLF Injection Vulnerability

published 2020-10-21 6 y ago modified 2026-08-11 2 mo ago also EUVD-2020-24832

cvss
4.7
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.3%
EPSS 1.3% chance of exploitation in 30 days, percentile 70%
public exploits
0
none known

Summary

A vulnerability in the Clientless SSL VPN (WebVPN) of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to inject arbitrary HTTP headers in the responses of the affected system. The vulnerability is due to improper input sanitization. An attacker could exploit this vulnerability by persuading a user of the interface to click a crafted link. A successful exploit could allow the attacker to conduct a CRLF injection attack, adding arbitrary HTTP headers in the responses of the system and redirecting the user to arbitrary websites.

Patch / fix

  • cisco adaptive_security_appliance 9.6.4.35
  • cisco secure_firewall_threat_defense 6.3.0.6, 6.4.0.10, 6.5.0.5, 6.6.1
  • cisco adaptive_security_appliance_software 9.8.4.20, 9.9.2.80, 9.10.1.43, 9.12.3.9, 9.13.1.10, 9.14.1.10

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
23 mo ago

Exploit prediction

1.27% chance of exploitation in the next 30 days, higher than 70% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.0 4.7 CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
NVD 3.1 4.7 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

  • Cisco Cisco Adaptive Security Appliance (ASA) Software

Classification

Weakness
  • CWE-93 Improper Neutralization of CRLF Sequences
  • CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.