Page data exfiltration via inherited CSP nonce
Published Mar 25, 2020 · Updated Aug 4, 2024
CSP bypass in Mozilla Firefox before 74 allows remote attackers to exfiltrate page data by injecting an @import rule into a nonced style block. Firefox's child-sheet loader reused the parent style element's CSP nonce, causing CheckContentSecurityPolicy to authorize an imported attacker stylesheet. Exploitation requires CSS injection into a nonce-protected page and a user to render it; the imported stylesheet can leak page content such as tokens.
Summary
What happened
CSP bypass in Mozilla Firefox before 74 allows remote attackers to exfiltrate page data by injecting an @import rule into a nonced style block. Firefox's child-sheet loader reused the parent style element's CSP nonce, causing CheckContentSecurityPolicy to authorize an imported attacker stylesheet. Exploitation requires CSS injection into a nonce-protected page and a user to render it; the imported stylesheet can leak page content such as tokens.
The record
- CVE
- CVE-2020-6813
- Published
- Mar 25, 2020
- Updated
- Aug 4, 2024
- Vendor
- Mozilla
- Product
- Firefox
- Classifications
- T1189
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 25, 2020CVE publishedPublication date reported by the CVE source.
- 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.
- Affected versionversion=unspecified <74
What conditions does exploitation require?
What is affected?
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
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Weakness, pattern, technique
Public exploit references
- Mozilla Bugzilla CSS @import proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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