CVE-2020-6820
Race Condition in Mozilla Firefox ≤ 68.6.1
Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HSummary
CVE-2020-6820 is a high-severity Race Condition (CWE-362) vulnerability in Mozilla Firefox. Its CVSS base score is 8.1 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 7% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2020-6820 is a race condition (CWE-362) that produces a use-after-free when a ReadableStream is handled under certain timing conditions. The flaw affects Mozilla Firefox before 74.0.1, Firefox ESR before 68.6.1, and Thunderbird before 68.7.0.
An unauthenticated remote attacker can trigger the vulnerability over the network with no user interaction required. Successful exploitation yields arbitrary code execution with full confidentiality, integrity, and availability impact, and the issue has already been observed in targeted attacks in the wild.
Mozilla security advisories MFSA2020-11 and MFSA2020-14, together with the corresponding Ubuntu update USN-4335-1, address the flaw by shipping corrected builds; users are advised to upgrade to the listed fixed versions. The high CVSS score of 8.1 reflects the combination of remote attack vector and severe consequences once the race is won.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2020-27964
Vulnerability Data
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.
- CWE(s)
- KEV Date Added
- 03 November 2021
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V10.4.2V10.4.5V15.1.3V15.4.1
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Accurate timestamps from internal clocks enable detection of race conditions by providing reliable event ordering in audit logs.
Coordination of concurrent security activities reduces the probability that shared resources will be accessed simultaneously without proper synchronization.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly require proper synchronization primitives and concurrency testing that prevent race conditions.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing can detect race conditions, but does not prevent them at design or coding time.
Secure SDLC mandates concurrency controls and synchronization primitives that directly prevent race conditions.
Application security requirements can specify thread-safety and locking rules, but do not prescribe implementation details.
Secure architecture principles require proper synchronization and resource isolation, addressing the root cause of CWE-362.
Secure coding standards explicitly forbid unsafe concurrent access patterns and mandate atomic operations or locks.
Change management reduces introduction of concurrency bugs during updates, yet does not address the weakness itself.