CVE-2021-29978Public exploitNetwork attack vector

Data exposure and update tampering via validation failures

Published Aug 5, 2021 · Updated Aug 3, 2024

Multiple security flaws in Mozilla VPN before 2.3 allow remote attackers to expose data, disrupt login, or tamper with updates. The grouped findings include incomplete update-certificate validation, an unauthenticated localhost WebSocket, an unprotected OAuth callback listener, verbose API errors, and a ping race outside the tunnel. Exploitation depends on the individual flaw and can require a malicious website, local reachability, a trusted certificate authority, authentication, or precise timing.

CVSS severity9.8
Critical
EPSS probability2.78%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Multiple security flaws in Mozilla VPN before 2.3 allow remote attackers to expose data, disrupt login, or tamper with updates. The grouped findings include incomplete update-certificate validation, an unauthenticated localhost WebSocket, an unprotected OAuth callback listener, verbose API errors, and a ping race outside the tunnel. Exploitation depends on the individual flaw and can require a malicious website, local reachability, a trusted certificate authority, authentication, or precise timing.

The record

CVE
CVE-2021-29978
Published
Aug 5, 2021
Updated
Aug 3, 2024
Vendor
Mozilla
Product
Mozilla VPN
Classifications
T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 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=unspecified <2.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Mozilla VPNversion=unspecified <2.3

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
10.0NIST NVDAV:N/AC:L/Au:N/C:C/I:C/A:C

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

T1557Adversary-in-the-Middle

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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