Mozilla Firefox, Firefox ESR, and Thunderbird Use-After-Free
CVE-2016-9079 is a high-severity use after free vulnerability in Firefox from Mozilla, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 50.0.2 as the first without the flaw, so updating Firefox to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on June 22, 2023, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Firefox to 50.0.2 or a later version.
- Update Firefox ESR to 45.5.1 or a later version.
- Update Thunderbird to 45.5.1 or a later version.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on bugzilla.mozilla.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Mozilla | Firefox | before 50.0.2 | 50.0.2 |
| Mozilla | Firefox ESR | before 45.5.1 | 45.5.1 |
| Mozilla | Thunderbird | before 45.5.1 | 45.5.1 |
| Debian | Debian Linux | 9.0 | Not stated |
| Red Hat | Enterprise Linux | 5.0; 6.0; 7.0 | Not stated |
| Red Hat | Enterprise Linux Desktop | 5.0; 6.0; 7.0 | Not stated |
| Red Hat | Enterprise Linux Server | 5.0; 6.0; 7.0 | Not stated |
| Red Hat | Enterprise Linux Server AUS | 7.3; 7.4 | Not stated |
| Red Hat | Enterprise Linux Server EUS | 7.3; 7.4; 7.5 | Not stated |
| Red Hat | Enterprise Linux Workstation | 5.0; 6.0; 7.0 | Not stated |
| Torproject | Tor | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | NVD |
| CVSS 3.1 | 7.5 | High | CISA (ADP) |
| CVSS 2.0 | 5.0 | Medium | NVD |
Official description
A use-after-free vulnerability in SVG Animation has been discovered. An exploit built on this vulnerability has been discovered in the wild targeting Firefox and Tor Browser users on Windows. This vulnerability affects Firefox < 50.0.2, Firefox ESR < 45.5.1, and Thunderbird < 45.5.1.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- bugzilla.mozilla.org/show_bug.cgi?id=1321066Exploit, Issue Tracking
- mozilla.org/security/advisories/mfsa2016-92/
Third-party and government advisories
- rhn.redhat.com/errata/RHSA-2016-2843.htmlThird Party Advisory
- rhn.redhat.com/errata/RHSA-2016-2850.htmlThird Party Advisory
- securitytracker.com/id/1037370Third Party Advisory, VDB Entry
- security.gentoo.org/glsa/201701-15Third Party Advisory
- security.gentoo.org/glsa/201701-35Third Party Advisory
- debian.org/security/2016/dsa-3730Third Party Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2016-9079US Government Resource
Technical write-ups (may include proof of concept)
- exploit-db.com/exploits/41151/Exploit, Third Party Advisory, VDB Entry
- exploit-db.com/exploits/42327/Exploit, Third Party Advisory, VDB Entry
Other vulnerabilities in Firefox
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
Recent Use After Free vulnerabilities
- 7.8 High severity
Adobe Flash Player Use-After-Free Exploited
- 7.8 High severity
Microsoft Win32k Privilege Escalation Exploited
- 7.8 High severity
Microsoft Office Use-After-Free Exploited
- 8.8 High severity
Adobe Flash Player Use-After-Free Exploited
- 8.8 High severity
Adobe Flash Player Use-After-Free Exploited
- 8.8 High severity
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