CVE-2021-40835Network attack vector

Address-bar spoofing via overlong URL username

Published Dec 16, 2021 · Updated Aug 4, 2024

URL address-bar spoofing in F-Secure Mobile Security 18.3 through 18.4 allows remote attackers to impersonate domains through crafted links. The iOS Safe Browser displays an attacker-controlled, overlong username portion of the URL, pushing the actual domain beyond the visible address-bar area. A user must open the link and trust the obscured address bar; the spoof misrepresents content origin but has no reported direct code-execution or availability impact.

CVSS severity4.6
Medium
EPSS probability0.70%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

URL address-bar spoofing in F-Secure Mobile Security 18.3 through 18.4 allows remote attackers to impersonate domains through crafted links. The iOS Safe Browser displays an attacker-controlled, overlong username portion of the URL, pushing the actual domain beyond the visible address-bar area. A user must open the link and trust the obscured address bar; the spoof misrepresents content origin but has no reported direct code-execution or availability impact.

The record

CVE
CVE-2021-40835
Published
Dec 16, 2021
Updated
Aug 4, 2024
Vendor
F-Secure
Product
F-Secure Mobile Security
Classifications
T1660
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=18.3 <18.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F-Secure · F-Secure Mobile Securityversion=18.3 <18.5

Published CVSS scores

4.3NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.6F-SecureCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/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

T1660Phishing

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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