CVE-2020-6820Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free.
Updated under an hour ago ()
Does this affect you?
It affects Mozilla Thunderbird and 2 other products. Add what you run to find out whether that includes you.
CISA lists it as known exploited since Nov 3, 2021; federal agencies had to remediate by May 3, 2022. Treat that date as your deadline.
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Free account, 1 product
Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Thunderbird < 68.7.0, Firefox < 74.0.1, and Firefox ESR < 68.6.1.
- CVSS
- 8.1 HIGH (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- CWE-362
- Known exploited
- Added to CISA KEV Nov 3, 2021; federal remediation due May 3, 2022Apply updates per vendor instructions.
- EPSS (exploitation in the next 30 days)
- 7.06% (percentile 94)
- Assigned by
- mozilla
- NVD analysis
- Analyzed
- Record last updated
- Oct 21, 2025
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Mozilla Thunderbird mozilla:thunderbird (from the name) | from unspecified before 68.7.0 | CNA record |
Mozilla Firefox mozilla:firefox (from the name) | from unspecified before 74.0.1 | CNA record |
Mozilla Firefox ESR mozilla:firefox_esr (from the name) | from unspecified before 68.6.1 | CNA record |
mozilla firefox mozilla:firefox | before 68.6.1; before 74.0.1 | NVD |
mozilla thunderbird mozilla:thunderbird | before 68.7.0 | NVD |
References
- https://www.mozilla.org/security/advisories/mfsa2020-14/x-refsource-misc, vendor-advisory
- https://www.mozilla.org/security/advisories/mfsa2020-11/x-refsource-misc, vendor-advisory
- https://bugzilla.mozilla.org/show_bug.cgi?id=1626728x-refsource-misc, issue-tracking, permissions-required
- https://usn.ubuntu.com/4335-1/vendor-advisory, x-refsource-ubuntu, third-party-advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-6820us-government-resource
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.