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:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2020-6820 is a high-severity Race Condition (CWE-362) vulnerability in Mozilla Firefox. Its CVSS base score is 8.1 (High).
Operationally, ranked in the top 6% 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
CVEs Like This One
Affected Assets
Mitigating Controls
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 (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.
A.8.25 mandates secure SDLC practices (secure coding guidelines, security requirements, checkpoints, testing including code scans/penetration tests, developer training) that reach race conditions in concurrent code, but only as one slice of a broad requirement whose implementation scope and rigour are left to the organisation.
A.8.26 explicitly lists resilience against malicious attacks including SQL injections and input validation as application security requirements to identify/address; race conditions are a similar class of timing-based concurrency flaw that can be mitigated by requirements for proper synchronization/locking, but this is only one slice of the broad CWE-362 class (most instances arise in low-level shared-memory or TOCTOU scenarios not named here).
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.
Security testing can detect race conditions, but does not prevent them at design or coding time.
Hardening callouts derived
DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.
- No fine-grained STIG row for CWE-362, a class-level weakness, and none of its children carries one either.