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CVE-2020-6820 (GCVE-0-2020-6820)

Vulnerability from cvelistv5 – Published: 2020-04-24 15:56 – Updated: 2025-10-21 23:35
VLAI CISA Previdian
Summary
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.
Severity
8.1 (High)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: active Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-02-07 12:49 UTC
CWE
  • Use-after-free when handling a ReadableStream
  • CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
Assigner
References
Impacted products
Vendor Product Version CPE status
Mozilla Thunderbird Affected: unspecified , < 68.7.0 (custom)
guessed Create a notification for this product.
Mozilla Firefox Affected: unspecified , < 74.0.1 (custom)
guessed Create a notification for this product.
Mozilla Firefox ESR Affected: unspecified , < 68.6.1 (custom)
guessed Create a notification for this product.
CISA
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: e1ec3321-729f-43d3-9d8c-1b7b00f0cc30

Vulnerability ID: CVE-2020-6820

Status: Confirmed

Status Updated: 2021-11-03 00:00 UTC

Exploited: Yes

Timestamps
First Seen: 2021-11-03
Asserted: 2021-11-03
Scope
Notes: KEV entry: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability | Affected: Mozilla / Firefox and Thunderbird | Description: Mozilla Firefox and Thunderbird contain a race condition vulnerability when handling a ReadableStream under certain conditions. The race condition creates a use-after-free vulnerability, causing unspecified impacts. | Required action: Apply updates per vendor instructions. | Due date: 2022-05-03 | Known ransomware campaign use (KEV): Unknown | Notes (KEV): https://nvd.nist.gov/vuln/detail/CVE-2020-6820
Evidence

Type: Vendor Report

Signal: Successful Exploitation

Confidence: 80%

Source: cisa-kev

Details
Cwes CWE-362
Feed CISA Known Exploited Vulnerabilities Catalog
Product Firefox and Thunderbird
Due Date 2022-05-03
Date Added 2021-11-03
Vendorproject Mozilla
Vulnerabilityname Mozilla Firefox And Thunderbird Use-After-Free Vulnerability
Knownransomwarecampaignuse Unknown
References
Created: 2026-02-02 12:28 UTC | Updated: 2026-02-06 07:17 UTC
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: bdfde996-0001-42bb-9c61-6b3b07061083

Vulnerability ID: CVE-2020-6820

Status: Confirmed

Status Updated: 2021-11-03 00:00 UTC

Exploited: Yes

Timestamps
First Seen: 2021-11-03
Asserted: 2021-11-03
Scope
Notes: KEVIntel entry: 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... | Affected: Mozilla / Thunderbird, Firefox, Firefox ESR | CVSS: 8.1 (HIGH) | Used in malware: unknown | Not yet in CISA KEV: False
Evidence

Type: Public Report

Signal: Successful Exploitation

Confidence: 70%

Source: kevintel

Details
Feed KEVIntel (kevintel.com)
Title 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...
Vendor Mozilla
Product Thunderbird, Firefox, Firefox ESR
Added Date 2021-11-03T00:00:00.000Z
Cvss Score 8.1
Epss Score None
Cvss Severity HIGH
Epss Percentile None
Used In Malware unknown
Ahead Of Cisa Kev None
Not Yet In Cisa Kev False
References
Created: 2026-06-23 14:04 UTC | Updated: 2026-07-10 06:14 UTC
Show details on NVD website
To clipboard 

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      "status": "final",
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      "version": "3"
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      "initial_release_date": "2023-02-15T04:02:06Z",
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      "product_status:recommended": "376",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2020-6820",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2020-6820.json",
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}



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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.