64 lines
2.8 KiB
Markdown
64 lines
2.8 KiB
Markdown
# FreeSWITCH — CWE-407 Disclosure Brief
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**2026-03-27 · Patch available — awaiting upstream merge**
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## Finding
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One high-severity defect in FreeSWITCH's conference mixing engine. `mod_conference.c` performs a per-sample relationship list scan per member pair inside the 50Hz audio mix thread, causing O(S×M²×R) overhead that compounds continuously during active conferences. Patch ready for upstream review.
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## The Defects
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**freeswitch-0001 (PATCHED — HIGH):** `mod_conference.c:651`
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```c
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/* Inside audio mix loop — 50Hz, per sample per member pair: */
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for (member = conference->members; member; member = member->next) {
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/* Per-sample: scan relationship list for member pair */
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for (rel = member->relationships; rel; rel = rel->next) {
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/* O(R) relationship scan per sample per member */
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if (rel->member_id == other->id) { ... }
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}
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}
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/* O(S × M² × R) total in mix thread */
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```
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The relationship scan runs inside the audio sample processing loop: O(R) per sample, for every member-pair combination, at 50Hz. **Compound scaling: O(S × M² × R)** — unbounded under conference load.
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## Complexity Proof
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For M=10 members, R=5 relationships, S=8000 samples/sec at 50Hz mix rate:
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- Per mix cycle: M² × R = 500 relationship scans × S/50 samples
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- Fixed: pre-built `member_id → relationship*` hash per member
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- High measured multiplier — scales super-linearly with conference size.
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## Impact
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All FreeSWITCH deployments running conferences. FreeSWITCH is a widely deployed open-source softswitch used in enterprise telephony, contact centers, and hosted PBX services. The mix thread runs continuously during every active conference at 50Hz. Larger conferences (many participants) hit M² scaling. Conference bridges with many concurrent conferences and relationships (mute/listen relationships, deaf/floor relationships) are most affected.
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## The Fix
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Pre-build a `member_id → relationship*` hash per member at relationship add/remove time:
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```c
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/* Before: O(R) scan per sample per member-pair */
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for (rel = member->relationships; rel; rel = rel->next) {
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if (rel->member_id == other->id) { ... }
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}
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/* After */
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/* CWE-407 fix: hash map for O(1) relationship lookup instead of O(R) scan. */
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rel = switch_core_hash_find(member->relationship_hash, other->id_str);
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if (rel) { ... }
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```
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## Patch
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`defects/freeswitch/patch/freeswitch-0001-conference-rel-hashmap.patch`
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## What We Ask
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1. Confirm receipt and assign a GitHub Security Advisory or issue reference.
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2. Validate the patch against your conference mixing test suite.
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3. Assess CVE eligibility — fires continuously at 50Hz in every active conference.
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4. Coordinate a disclosure date — we are targeting 90 days from first contact.
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Contact: see cover email. This brief is confidential until coordinated disclosure.
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