[UPDATE] [high] Mozilla Firefox: Multiple vulnerabilities

highCVE-2026-8388 CVE-2026-8389 CVE-2026-8390 CVE-2026-8391 CVE-2026-8401

A remote, anonymous attacker can exploit multiple vulnerabilities in Mozilla Firefox to conduct unspecified attacks, potentially including code execution, bypassing security measures, disclosing or manipulating data, or causing Denial-of-Service conditions.

CSIRTS triage

vendor: Mozilla product: Firefox Remote code execution Authentication bypass Information disclosure Denial of serviceOther

What: Multiple vulnerabilities can be exploited to conduct unspecified attacks, potentially including code execution and data manipulation.
Who is affected: Users of Mozilla Firefox are affected.
Urgency: Remediation is urgent due to the high severity and potential for exploitation.
Action: Update to the latest version of Mozilla Firefox.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: CERT-Bund (BSI) Security Advisories (DE · national-cert · site)
Severity: high
Published: 2026-07-09
Exploitation: Not in CISA KEV at last sync
Language: Machine-translated to English — verify against the original

Original advisory: https://wid.cert-bund.de/portal/wid/securityadvisory?name=WID-SEC-2026-1503

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-83880.24% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 15% of all scored CVEs.
Low exploitation riskCVE-2026-83890.33% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 25% of all scored CVEs.
Low exploitation riskCVE-2026-83900.26% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 17% of all scored CVEs.
Low exploitation riskCVE-2026-83910.30% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 22% of all scored CVEs.
Low exploitation riskCVE-2026-84010.31% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 23% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-8388	coverage & exploitation status	NVD · CVE.org
CVE-2026-8389	coverage & exploitation status	NVD · CVE.org
CVE-2026-8390	coverage & exploitation status	NVD · CVE.org
CVE-2026-8391	coverage & exploitation status	NVD · CVE.org
CVE-2026-8401	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

high[UPDATE] [high] Mozilla Firefox and Thunderbird: Multiple vulnerabilitiescert-bund

Recent advisories for Mozilla Firefox

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

high[UPDATE] [high] Mozilla Firefox, Firefox ESR and Thunderbird: Multiple vulnerabilitiescert-bund · 2026-07-10
high[UPDATE] [high] Mozilla Firefox and Thunderbird: Multiple vulnerabilitiescert-bund · 2026-07-09
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