CVE-2020-6820
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Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free
rank 71 = 40 + 20 + 0 + 5 + 6
rank@v1 · act now
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.07063 · CISA KEV listed · without this subject the record ranks 31
What it costs you if it fires
NVD CVSS base score, then the CNA's own
CVSS 8.1, from NVD · without this subject the record ranks 51
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
no persisting rise in 365 days · without this subject the record ranks 71
How much of the world it touches
NVD CPE configurations
3 products in the CPE ranges · without this subject the record ranks 66
Someone else already set the date
CISA KEV remediation due date
CISA remediation date held · without this subject the record ranks 65
$352,000 = $4.99M incident cost x 1 exposure x 0.07063 likelihood
udv@v1 · unaudited · wrong for you until you say what you run
$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.
Hindsight · the state
Foresight · where to check next
This record is one instance of CWE-362, concurrent execution using shared resource with improper synchronization ('race condition'). The index holds 2679 prior instances of this class, 11 KEV-listed. The nearest of its KEV-listed records are drawn beside this. taxonomy@v1
Running Mozilla Thunderbird? Check your version
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Harm, if it fires from the vector and the weakness
Written for the ticket you're about to file.
CISA KEV & Federal Remediation Deadline from the record and CISA
The fix, and how long it's been waiting.
Exploit Status & Known PoCs a ladder, not a score
Current rung: Exploited in the wild · CISA KEV listed, 2021-11-03.
- RUNG 1Nothing observed in held sources
- RUNG 2Proof-of-concept published
- RUNG 3Exploited in the wild · CISA KEV listed2021-11-03receipt
- RUNG 4Ransomware campaign use known
A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.
What it is stated by the CNA
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. receipt
NVD's analysis a second authority
- severity
- 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- weakness
- CWE-362
- affected versions
- mozilla firefox < 68.6.1; mozilla firefox < 74.0.1; mozilla thunderbird < 68.7.0
- also scored by
- 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
check it yourself mozilla.org mozilla.org bugzilla.mozilla.org usn.ubuntu.com receipt
Dated events
Movement the material steps
Show all 26 observations
26 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt
The pattern, elsewhere
This record is one instance of CWE-362, concurrent execution using shared resource with improper synchronization ('race condition'). The index holds 2679 prior instances of this class, 11 KEV-listed. The nearest of its KEV-listed records are drawn beside this. [email protected]
"Matches n of m" counts the attributes the two records can both be compared on: the CVSS metrics they share a version of, any weakness class beyond this one, and the vendor. fit-rules@v1
2679 records in this class held. The six above are drawn from the ones CISA has listed as exploited, ranked by how much of the record matches this one. That is why every one of them is KEV-listed: the pool is, so the colour on those spokes says nothing the pool has not already said.
No curated product neighbourhood is held for this product, so the records above are the nearest this index can name. The neighbourhood table covers a small set of products and is extended by hand.
Siblings and hubs
Records related to this one
No record cites this identifier and it carries no alias. Its defect family is below.
Its defect family
mozilla thunderbird
Of the 9 records in this family that state one, this holds the highest EPSS percentile: 0.93757.
Grouped by shared product and weakness, not by shared vulnerability. Each record's own state is on its own page.
Family membership: held values
This record is one of a group, and the group's page describes all of them. This page is kept and dated, and the defect family's own page is the one we offer for indexing: the whole group.
Browse the index from here
These are index-wide views, not findings about CVE-2020-6820.
What usually comes next
Everything above needs no account. What is below is work: assembling it, scoping it to your estate, watching it, and handing it to someone else.