Use-after-free in the DOM: HTML Parser component
Affects Firefox and is fixed in Firefox 160. CVSS scores it 8.8 High, and Mozilla has not published a separate vendor severity rating.
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
Use-after-free in the DOM: HTML Parser 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
- Severity9.8/10CVSS 8.8, 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
Affected versions
- Mozilla Firefox
Version range not reported
Evidence 2
- Link
- Link
Corrections
None so far.
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Questions about CVE-2026-124871
Is CVE-2026-124871 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 HTML parser of Firefox's DOM, which corrupts memory. Mozilla rates it high impact, but the advisory does not describe what an attacker could gain.Source: mozilla.org
Am I affected, and how do I check?
The facts list Firefox as the product but give no affected version range or setup conditions. To check a installation, compare its Firefox version with the fixed release, Firefox 160.Source: mozilla.org
How do I fix CVE-2026-124871?
Update Firefox to version 160 or later, which contains the fix. No workaround is listed in the facts.Source: mozilla.org