CVE-2026-8971
published 2026-05-19CVE-2026-8971: Same-origin policy bypass in the Networking: JAR component. This vulnerability was fixed in Firefox 151 and Thunderbird 151.
PriorityP433medium6.5CVSS 3.1
AVNACLPRNUINSUCLILAN
EPSS
0.21%
10.5th percentile
Same-origin policy bypass in the Networking: JAR component. This vulnerability was fixed in Firefox 151 and Thunderbird 151.
Affected
4 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| mozilla | firefox | < Firefox 151 | Firefox 151 |
| mozilla | firefox | < 151.0.0 | 151.0.0 |
| mozilla | thunderbird | < Thunderbird 151 | Thunderbird 151 |
| mozilla | thunderbird | < 151.0.0 | 151.0.0 |
CVSS provenance
nvdv3.16.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
vendor_redhat6.5MEDIUM
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Red Hat
firefox: thunderbird: Same-origin policy bypass in the Networking: JAR component
vendor_redhat·2026-05-19·CVSS 6.5
CVE-2026-8971 [MEDIUM] CWE-346 firefox: thunderbird: Same-origin policy bypass in the Networking: JAR component
firefox: thunderbird: Same-origin policy bypass in the Networking: JAR component
Same-origin policy bypass in the Networking: JAR component. This vulnerability was fixed in Firefox 151 and Thunderbird 151.
A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue:
Same-origin policy bypass in the Networking: JAR component
Statement: Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.
Package: firefox (Red Hat Enterprise Linux 10) - Not affected
Package: rhel10/firefox-flatpak (Red Hat Enterprise Linux 10) - Not affected
Package: rhel10/thunderbird-flatpak (Red Hat Enterprise Linux 10) - Not affected
Package: thunderbird (Red Hat Enterprise Linux 10) - Not affec
Mozilla
Mozilla Foundation Security Advisory 2026-46: CVE-2026-8971
vendor_mozilla·CVSS 6.5
CVE-2026-8971 [MEDIUM] Mozilla Foundation Security Advisory 2026-46: CVE-2026-8971
Mozilla Foundation Security Advisory 2026-46
CVE: CVE-2026-8971
Product: Firefox
Impact: high
Fixed in: Firefox 151
Mozilla
Mozilla Foundation Security Advisory 2026-50: CVE-2026-8971
vendor_mozilla·CVSS 6.5
CVE-2026-8971 [MEDIUM] Mozilla Foundation Security Advisory 2026-50: CVE-2026-8971
Mozilla Foundation Security Advisory 2026-50
CVE: CVE-2026-8971
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 151
GHSA
GHSA-wg2h-wc56-7jcc: Same-origin policy bypass in the Networking: JAR component
ghsa_unreviewed·2026-05-19
CVE-2026-8971 [MEDIUM] CWE-346 GHSA-wg2h-wc56-7jcc: Same-origin policy bypass in the Networking: JAR component
Same-origin policy bypass in the Networking: JAR component. This vulnerability was fixed in Firefox 151.
VulDB
Mozilla Firefox up to 150 JAR cross-domain policy (EUVD-2026-30919)
vuldb·2026-05-19·CVSS 6.5
CVE-2026-8971 [MEDIUM] Mozilla Firefox up to 150 JAR cross-domain policy (EUVD-2026-30919)
A vulnerability identified as problematic has been detected in Mozilla Firefox up to 150. This impacts an unknown function of the component JAR. This manipulation causes permissive cross-domain policy with untrusted domains.
This vulnerability is handled as CVE-2026-8971. The attack can be initiated remotely. There is not any exploit available.
You should upgrade the affected component.
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-8971 firefox: thunderbird: Same-origin policy bypass in the Networking: JAR component
bugzilla·2026-05-19·CVSS 6.5
CVE-2026-8971 [MEDIUM] CVE-2026-8971 firefox: thunderbird: Same-origin policy bypass in the Networking: JAR component
CVE-2026-8971 firefox: thunderbird: Same-origin policy bypass in the Networking: JAR component
Same-origin policy bypass in the Networking: JAR component. This vulnerability was fixed in Firefox 151.
Bugzilla
jar: URL %00 still enables download filename spoofing & MIME confusion via resource:// — incomplete fix for CVE-2025-1936 / CVE-2026-2790
bugzilla·2026-04-16·CVSS 7.3
CVE-2025-1936 [HIGH] jar: URL %00 still enables download filename spoofing & MIME confusion via resource:// — incomplete fix for CVE-2025-1936 / CVE-2026-2790
jar: URL %00 still enables download filename spoofing & MIME confusion via resource:// — incomplete fix for CVE-2025-1936 / CVE-2026-2790
Created attachment 9570825
test.zip
## Background
This is a **third bug in the same vulnerability class** in Firefox's `jar:` URL
protocol handler. The two prior bugs in this chain are:
- **CVE-2025-1936** (Bug 1940027) — Single `%00` in `jar:` URL caused `strlen()`
truncation in `nsZipArchive::GetItem`, mismatching the loaded file vs applied
MIME type. Fixed by replacing `char*` / `strlen` with `nsACString`.
- **CVE-2026-2790** (Bug 2008426)— Double-encoded `%2500` bypassed the `nsACString` fix because
`%2500` decoded to `%00` (not `\0`) in one pass. Fixed by disabling content
sniffing for JAR channels entirely.
**Neither fix added upfront rejectio
2026-05-19
Published