# RHSA-2021:4123: firefox security update

RHSA-2021:4123, released November 3, 2021, fixes 8 CVEs in firefox (version 0:91.3.0-1.el8_4). None of them is reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/fix/linux/rhsa-2021-4123
- Platform: Linux
- Released: Nov 3, 2021
- Priority: High (Closes CVE-2021-38503, high severity)
- CVEs: 8, exploited: 0, on CISA KEV: 0
- Vendor advisory: https://access.redhat.com/errata/RHSA-2021:4123

## Applies to

| Product | Release | Fixed in |
|---|---|---|
| [firefox](https://patchblox.com/security/data/product/linux/firefox.md) | RHEL 8 | 0:91.3.0-1.el8_4 |

## CVEs this fix closes

| CVE | Priority | Title | CVSS | EPSS | Exploitation |
|---|---|---|---:|---:|---|
| [CVE-2021-38503](https://patchblox.com/security/data/cve/CVE-2021-38503.md) | High | Mozilla Firefox ESR and 3 others: The iframe sandbox rules were not correctly applied to XSLT stylesheets, allowing an iframe to bypass… | 10.0 | 0.0412 |  |
| [CVE-2021-38504](https://patchblox.com/security/data/cve/CVE-2021-38504.md) | High | Mozilla Firefox ESR and 3 others: When interacting with an HTML input element's file picker dialog with webkitdirectory set, a use-after-free… | 9.8 | 0.0177 |  |
| [CVE-2021-38506](https://patchblox.com/security/data/cve/CVE-2021-38506.md) | High | Mozilla Firefox ESR and 3 others: Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning… | 7.5 | 0.0151 |  |
| [CVE-2021-43534](https://patchblox.com/security/data/cve/CVE-2021-43534.md) | High | Mozilla Firefox ESR and 3 others: Mozilla developers and community members reported memory safety bugs present in Firefox 93 and Firefox… | 8.8 | 0.0125 |  |
| [CVE-2021-43535](https://patchblox.com/security/data/cve/CVE-2021-43535.md) | High | Mozilla Firefox ESR and 3 others: A use-after-free could have occured when an HTTP2 session object was released on a different thread,… | 8.8 | 0.0115 |  |
| [CVE-2021-38507](https://patchblox.com/security/data/cve/CVE-2021-38507.md) | High | Mozilla Firefox ESR and 3 others: The Opportunistic Encryption feature of HTTP2 (RFC 8164) allows a connection to be transparently upgraded… | 7.5 | 0.0083 |  |
| [CVE-2021-38509](https://patchblox.com/security/data/cve/CVE-2021-38509.md) | Routine | Mozilla Firefox ESR and 3 others: Due to an unusual sequence of attacker-controlled events, a Javascript alert() dialog with arbitrary… | 6.1 | 0.0176 |  |
| [CVE-2021-38508](https://patchblox.com/security/data/cve/CVE-2021-38508.md) | Routine | Mozilla Firefox ESR and 3 others: By displaying a form validity message in the correct location at the same time as a permission prompt… | 6.1 | 0.0164 |  |

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Data as of 2026-11-07T18:46:35Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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