CVE-2021-33600Network attack vector

Service interruption via oversized username assertion

Published Sep 28, 2021 · Updated Aug 3, 2024

Reachable assertion in F-Secure Internet Gatekeeper 5 Series allows remote attackers to interrupt service through its web interface. The interface accepts an oversized username in a malformed HTTP packet and reaches an assertion, interrupting product availability. No authentication or user interaction is required, and public sources do not distinguish a web-interface outage from interruption of the full gateway.

CVSS severity7.5
High
EPSS probability0.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reachable assertion in F-Secure Internet Gatekeeper 5 Series allows remote attackers to interrupt service through its web interface. The interface accepts an oversized username in a malformed HTTP packet and reaches an assertion, interrupting product availability. No authentication or user interaction is required, and public sources do not distinguish a web-interface outage from interruption of the full gateway.

The record

CVE
CVE-2021-33600
Published
Sep 28, 2021
Updated
Aug 3, 2024
Vendor
F-Secure
Product
F-Secure Internet Gatekeeper
Classifications
CWE-617, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5 Series All Version

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F-Secure · F-Secure Internet Gatekeeperversion=5 Series All Version

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
5.4F-SecureCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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