CVE-2021-29958Public exploitNetwork attack vector

Private-mode cookie disclosure via download context mix-up

Published Jun 24, 2021 · Updated Aug 3, 2024

Information disclosure in Firefox for iOS before 34 allows remote attackers to obtain private-mode cookies through file downloads. DownloadQueue's Swift-side HTTP client sends the download request without preserving whether its originating tab uses private browsing, allowing its cookie state to cross into normal browsing. Exploitation requires a user to set a cookie in private mode, revisit the same site normally, and initiate a download; the resulting disclosure is limited to cookies sent with that request.

CVSS severityUnavailable
Unscored
EPSS probability0.67%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Firefox for iOS before 34 allows remote attackers to obtain private-mode cookies through file downloads. DownloadQueue's Swift-side HTTP client sends the download request without preserving whether its originating tab uses private browsing, allowing its cookie state to cross into normal browsing. Exploitation requires a user to set a cookie in private mode, revisit the same site normally, and initiate a download; the resulting disclosure is limited to cookies sent with that request.

The record

CVE
CVE-2021-29958
Published
Jun 24, 2021
Updated
Aug 3, 2024
Vendor
Mozilla
Product
Firefox for iOS
Classifications
T1539
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 24, 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 <34

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefox for iOSversion=unspecified <34

Published CVSS scores

No CVSS assessment is available in this record.

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 exploitPublished

Weakness, pattern, technique

T1539Steal Web Session Cookie

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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