CVE-2023-5173

What it actually does

Integer overflow triggered by network traffic under non-standard Alternate Services configuration leads to out-of-bounds write into privileged process memory.

Why it matters to the business

Potential browser memory corruption that could allow unauthorized modification of process data on affected systems, increasing risk of further compromise if the non-standard preference remains enabled.

How an attack unfolds

An attacker sends crafted network responses containing Alternate Services data that trigger the integer overflow when the non-standard preference is enabled, resulting in an out-of-bounds write to privileged memory.

How to fix it

Upgrade Mozilla Firefox to version 118 or later. Disable the non-standard preference network.http.altsvc.oe if it is not required.

How to confirm the fix worked

Verify installed Firefox version is 118 or higher and confirm the preference network.http.altsvc.oe is set to its default disabled state.

Typical attack path

1. Confirm target has non-standard preference network.http.altsvc.oe enabled
2. Craft malicious network traffic or webpage response to trigger integer overflow
3. Achieve out-of-bounds write into privileged process memory
4. Leverage corruption for further attacker-controlled actions

How to detect it

Review browser process memory for unexpected writes after Alternate Services traffic, inspect logs for non-standard Alternate Services usage, and check configuration for the enabling preference.

• network.http.altsvc.oe=true

What your security team should do

• Upgrade all Firefox deployments to version 118 or later immediately
• Audit environments for the non-standard preference network.http.altsvc.oe and disable where possible
• Monitor EPSS trend for continued increase and reassess prioritization