CVE-2021-21354Public exploitNetwork attack vector

User redirection via scheme-relative Location header

Published Mar 8, 2021 · Updated Aug 3, 2024

Open redirect in Mozilla PollBot before 1.4.4 allows remote attackers to send users to malicious sites through crafted URL paths. The handle_404 middleware passed a slash-trimmed request.path directly to HTTPFound, causing a path beginning with two slashes to become a scheme-relative Location header. Exploitation requires a user to follow an attacker-crafted PollBot URL; the redirect can deliver that user to any attacker-selected site.

CVSS severity6.1
Medium
EPSS probability1.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Open redirect in Mozilla PollBot before 1.4.4 allows remote attackers to send users to malicious sites through crafted URL paths. The handle_404 middleware passed a slash-trimmed request.path directly to HTTPFound, causing a path beginning with two slashes to become a scheme-relative Location header. Exploitation requires a user to follow an attacker-crafted PollBot URL; the redirect can deliver that user to any attacker-selected site.

The record

CVE
CVE-2021-21354
Published
Mar 8, 2021
Updated
Aug 3, 2024
Vendor
Mozilla
Product
PollBot
Classifications
CWE-601, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 8, 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=< 1.4.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · PollBotversion=< 1.4.4

Published CVSS scores

7.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:H/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
5.8NIST NVDAV:N/AC:M/Au:N/C:P/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.

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

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 exploitPublished

Weakness, pattern, technique

CWE-601URL Redirection to Untrusted Site ('Open Redirect')
T1204.001User Execution: Malicious Link

Public exploit references

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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