Sandbox escape due to use-after-free in the DOM: Service Workers component
Affects Firefox, with the fix listed in Firefox 160. No affected version range is published, and Mozilla gives no separate vendor rating alongside the CVSS score of 9.6.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in Firefox 160
- Who is exposed
- Specific setups only
Do first: Upgrade to a fixed version: Firefox 160.
- Published
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 22/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: no
- Technical impact: total
Summary
Sandbox escape due to use-after-free in the DOM: Service Workers component. This vulnerability was fixed in Firefox 160.
cve.now Index
- Exploitation0/40No signal
- Exposure12/25Specific setups only, reachable over the network without a login
- Reach?/20Unknown. No tracked technology or package matched
- Severity10/10CVSS 9.6, total technical impact per CISA
- No patch0/5No signal
What would change the score
- Would score about 72 if added to CISA KEV
- Would score about 67 if CISA's SSVC rates exploitation active
What to do
Upgrade to a fixed version: Firefox 160.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: total
- Record last updated
- Posted on X by cve.now
Affected versions
- Mozilla Firefox
Version range not reported
Evidence 2
- Link
- Link
Corrections
None so far.
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Questions about CVE-2026-124900
Is CVE-2026-124900 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
The bug is a use-after-free in the DOM Service Workers component of Firefox, which can allow a sandbox escape, reaching beyond the browser sandbox.Source: mozilla.org
Am I affected, and how do I check?
The published data lists Firefox with no affected version range. To check a installed version, open the Firefox About page from the menu, which shows the version number.Source: mozilla.org
How do I fix CVE-2026-124900?
Update Firefox to version 160 or later, the release that lists the fix.Source: mozilla.org