CVE-2020-3246Network attack vector

HTTP response header injection via unvalidated URL input

Published May 6, 2020 · Updated Nov 15, 2024

CRLF injection in the Cisco Umbrella web server allows remote attackers to inject arbitrary HTTP response headers through a crafted URL. The web server insufficiently validates URL input, allowing carriage-return and line-feed characters to become header delimiters in responses sent to a user's browser. Exploitation requires a user to open the crafted URL, and the established consequence is modification of response headers rather than server compromise.

CVSS severity4.7
Medium
EPSS probability0.90%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

CRLF injection in the Cisco Umbrella web server allows remote attackers to inject arbitrary HTTP response headers through a crafted URL. The web server insufficiently validates URL input, allowing carriage-return and line-feed characters to become header delimiters in responses sent to a user's browser. Exploitation requires a user to open the crafted URL, and the established consequence is modification of response headers rather than server compromise.

The record

CVE
CVE-2020-3246
Published
May 6, 2020
Updated
Nov 15, 2024
Vendor
Cisco Systems, Inc.
Product
Cisco Umbrella
Classifications
CWE-74, CWE-93, CAPEC-15, CAPEC-81
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 6, 2020CVE publishedPublication date reported by the CVE source.
  2. Nov 15, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cisco Systems, Inc. · Cisco Umbrellaversion=n/a

Published CVSS scores

4.3NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
4.7Cisco Systems, Inc.CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N/E:X/RL:X/RC:X
4.3NISTAV:N/AC:M/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
CWE-93Improper Neutralization of CRLF Sequences ('CRLF Injection')
CAPEC-15Command Delimiters
CAPEC-81Web Server Logs Tampering

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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