CVE-2020-12387: A race condition when running shutdown code for Web Worker led to a use-after-free vulnerability.
Noroxi assessment
Priority: Monitor (action score 32/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 1.4% (FIRST EPSS); higher than 73.3% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- Fixed version: firefox-esr (Alpine:v3.11) 68.8.0-r0; firefox (Alpine:v3.12) 76.0-r0; mozjs68 (Alpine:v3.12) 68.8.0-r0.
- Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Low priority for now. Upgrade to firefox-esr (Alpine:v3.11) 68.8.0-r0; firefox (Alpine:v3.12) 76.0-r0; mozjs68 (Alpine:v3.12) 68.8.0-r0 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
A race condition when running shutdown code for Web Worker led to a use-after-free vulnerability. This resulted in a potentially exploitable crash. This vulnerability affects Firefox ESR < 68.8, Firefox < 76, and Thunderbird < 68.8.0.
- BDU:2020-03820
- DLA-2205-1
- DLA-2206-1
- DSA-4678-1
- DSA-4683-1
- openSUSE-SU-2020:0621-1
- openSUSE-SU-2020:0643-1
- RHSA-2020:2031
- RHSA-2020:2032
- RHSA-2020:2033
- RHSA-2020:2036
- RHSA-2020:2037
- RHSA-2020:2046
- RHSA-2020:2047
- RHSA-2020:2048
- RHSA-2020:2049
- RHSA-2020:2050
- SUSE-SU-2020:1209-1
- SUSE-SU-2020:1218-1
- SUSE-SU-2020:1225-1
- Published
- May 26, 2020
- Updated
- Jun 16, 2026
- EPSS
- 1.4% · 73th percentile
- CWE
- CWE-362
Report tools
Action score
32
Monitor
Low priority for now.
- CVSS
- 32 / 40 · 8.1 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 1.4%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
Is your version affected? Check itNoroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| mozilla | firefox | cpe:2.3:a:mozilla:firefox |
| mozilla | firefox esr | cpe:2.3:a:mozilla:firefox_esr |
| mozilla | thunderbird | cpe:2.3:a:mozilla:thunderbird |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- mozilla firefoxbefore 76.0
- mozilla firefox esrbefore 68.8.0
- mozilla thunderbirdbefore 68.8.0
Versions reported by the vendor
Affected version ranges reported by the assigning authority (mozilla). Independent of NVD's CPE analysis and usually ahead of it.
Mozilla Firefox
- unspecified and later · before 76affected
Mozilla Firefox ESR
- unspecified and later · before 68.8affected
Mozilla Thunderbird
- unspecified and later · before 68.8.0affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Alpine:v3.11 | firefox-esr | before 68.8.0-r0 | 68.8.0-r0 |
| Alpine:v3.12 | firefox | before 76.0-r0 | 76.0-r0 |
| Alpine:v3.12 | mozjs68 | before 68.8.0-r0 | 68.8.0-r0 |
| Alpine:v3.16 | thunderbird | before 68.8.0-r0 | 68.8.0-r0 |
| Alpine:v3.21 | librewolf | before 76.0-r0 | 76.0-r0 |
| Debian:10 | firefox-esr | before 68.8.0esr-1~deb10u1 | 68.8.0esr-1~deb10u1 |
| Debian:10 | thunderbird | before 1:68.8.0-1~deb10u1 | 1:68.8.0-1~deb10u1 |
| Debian:12 | firefox-esr | before 68.8.0esr-1 | 68.8.0esr-1 |
| Debian:12 | thunderbird | before 1:68.8.0-1 | 1:68.8.0-1 |
| Debian:8 | firefox-esr | before 68.8.0esr-1~deb8u1 | 68.8.0esr-1~deb8u1 |
| Debian:8 | thunderbird | before 1:68.8.0-1~deb8u1 | 1:68.8.0-1~deb8u1 |
| Debian:9 | firefox-esr | before 68.8.0esr-1~deb9u1 | 68.8.0esr-1~deb9u1 |
| Debian:9 | thunderbird | before 1:68.8.0-1~deb9u1 | 1:68.8.0-1~deb9u1 |
| openSUSE:Leap 15.1 | MozillaFirefox | before 68.8.0-lp151.2.45.1 | 68.8.0-lp151.2.45.1 |
| openSUSE:Leap 15.1 | MozillaThunderbird | before 68.8.0-lp151.2.38.2 | 68.8.0-lp151.2.38.2 |
| Red Hat:enterprise_linux:6::client | firefox | before 0:68.8.0-1.el6_10 | 0:68.8.0-1.el6_10 |
| Red Hat:enterprise_linux:6::client | firefox-debuginfo | before 0:68.8.0-1.el6_10 | 0:68.8.0-1.el6_10 |
| Red Hat:enterprise_linux:6::client | thunderbird | before 0:68.8.0-1.el6_10 | 0:68.8.0-1.el6_10 |
| Red Hat:enterprise_linux:6::client | thunderbird-debuginfo | before 0:68.8.0-1.el6_10 | 0:68.8.0-1.el6_10 |
| Red Hat:enterprise_linux:7::client | firefox | before 0:68.8.0-1.el7_8 | 0:68.8.0-1.el7_8 |
| Red Hat:enterprise_linux:7::client | firefox-debuginfo | before 0:68.8.0-1.el7_8 | 0:68.8.0-1.el7_8 |
| Red Hat:enterprise_linux:7::client | thunderbird | before 0:68.8.0-1.el7_8 | 0:68.8.0-1.el7_8 |
| Red Hat:enterprise_linux:7::client | thunderbird-debuginfo | before 0:68.8.0-1.el7_8 | 0:68.8.0-1.el7_8 |
| Red Hat:enterprise_linux:8::appstream | firefox | before 0:68.8.0-1.el8_2 | 0:68.8.0-1.el8_2 |
+21
Same product
mozilla: all recordsOther highest-scoring records for the same primary product.
- CVE-2010-3765Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x…KEV94Now
- CVE-2019-11708Insufficient vetting of parameters passed with the Prompt:Open IPC message between child and parent processes can result in the…KEV87Now
- CVE-2015-4495The PDF reader in Mozilla Firefox before 39.0.3, Firefox ESR 38.x before 38.1.1, and Firefox OS before 2.2 allows remote attackers to…KEV86Now
Published before and after this one in the same product
- ← EarlierCVE-2020-12395May 26, 2020 · Mozilla developers and community members reported memory safety bugs present in Firefox 75 and Firefox ESR 68.7.40Plan
- ← EarlierCVE-2020-12396May 26, 2020 · Mozilla developers and community members reported memory safety bugs present in Firefox 75.40Plan
- Later →CVE-2020-12388May 26, 2020 · The Firefox content processes did not sufficiently lockdown access control which could result in a sandbox escape.41Plan
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| alpine:firefox | 76.0-r0 · Alpine:v3.12 | Package registry (OSV) |
| alpine:firefox-esr | 68.8.0-r0 · Alpine:v3.11 | Package registry (OSV) |
| alpine:librewolf | 76.0-r0 · Alpine:v3.21 | Package registry (OSV) |
| alpine:mozjs68 | 68.8.0-r0 · Alpine:v3.12 | Package registry (OSV) |
| alpine:thunderbird | 68.8.0-r0 · Alpine:v3.16 | Package registry (OSV) |
| debian:firefox-esr | 68.8.0esr-1 · Debian:12 | Package registry (OSV) |
| debian:thunderbird | 1:68.8.0-1 · Debian:12 | Package registry (OSV) |
| opensuse:MozillaFirefox | 68.8.0-lp151.2.45.1 · openSUSE:Leap 15.1 | Package registry (OSV) |
| opensuse:MozillaThunderbird | 68.8.0-lp151.2.38.2 · openSUSE:Leap 15.1 | Package registry (OSV) |
| red hat:firefox | 0:68.8.0-1.el8_2 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:firefox-debuginfo | 0:68.8.0-1.el8_2 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:firefox-debugsource | 0:68.8.0-1.el8_2 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:thunderbird | 0:68.8.0-1.el8_2 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:thunderbird-debuginfo | 0:68.8.0-1.el8_2 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:thunderbird-debugsource | 0:68.8.0-1.el8_2 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| suse:MozillaFirefox | 68.8.0-3.87.1 · SUSE:Linux Enterprise Module for Desktop Applications 15 SP1 | Package registry (OSV) |
| suse:MozillaThunderbird | 68.8.0-3.80.2 · SUSE:Linux Enterprise Workstation Extension 15 SP1 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-20-519 · Jul 13, 2020(IBM Ürünleri Güvenlik Güncellemesi)
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
Weakness class (CWE)
CWE-362 · Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
—
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (6 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.