CVE-2017-7805

What it actually does

Use-after-free triggered during TLS 1.2 handshake hash calculations when the transcript exceeds the current message buffer, causing reallocation that leaves a dangling pointer to freed memory and results in a crash.

Why it matters to the business

Unexpected crashes in browser and email clients during secure connections can interrupt user workflows, reduce availability of client applications, and create potential for further compromise if the freed memory is attacker-controlled.

How an attack unfolds

An attacker positions themselves as a TLS server or performs a man-in-the-middle attack on a TLS 1.2 session; they craft a handshake whose transcript size forces buffer reallocation, then trigger subsequent hash operations that dereference the stale pointer to achieve a crash or attempt memory corruption for code execution.

How to fix it

Upgrade Mozilla Firefox to version 56 or later, Firefox ESR to 52.4 or later, and Thunderbird to 52.4 or later; apply all subsequent security updates promptly; disable TLS 1.2 where feasible only as a temporary workaround.

How to confirm the fix worked

Inspect installed product versions against the affected ranges; review release notes for the specific TLS handshake fix; perform controlled TLS 1.2 handshakes with large transcripts in a test environment to confirm absence of crashes.

Typical attack path

1. Establish a TLS 1.2 connection to the vulnerable client
2. Send a handshake sequence large enough to exceed the active message buffer
3. Force allocation of a new buffer while retaining a pointer to the now-freed original buffer
4. Continue the handshake to invoke hash calculations that use the dangling pointer
5. Leverage the resulting memory state for crash or memory corruption primitives

How to detect it

Review application crash logs and memory dumps for faults occurring inside TLS handshake hash routines; correlate client connection attempts to untrusted servers immediately preceding crashes; examine system logs for repeated TLS session terminations without clear network cause.

What your security team should do

• Prioritize patching all instances of affected Mozilla products to the minimum fixed versions
• Inventory environments for legacy Firefox ESR and Thunderbird deployments
• Monitor vendor advisories for any follow-on patches addressing related handshake issues
• Consider network-level TLS inspection or proxying to reduce direct exposure until upgrades complete