Listen to this Post
CVE‑2026‑49841 affects FreeSWITCH, a software‑defined telecom stack that replaces proprietary switches with a commodity‑hardware implementation. Prior to version 1.11.1, the `mod_verto` HTTP request handler exhibits a critical heap‑based buffer overflow.
The vulnerability stems from a mismatch between the allocated buffer size and the accepted request length. The handler allocates a fixed 2 MiB buffer for an HTTP POST body with Content‑Type application/x‑www‑form‑urlencoded. However, it accepts a Content‑Length header up to nearly 10 MiB (just under 10 MiB). The body‑read loop is bounded by the Content‑Length value, not by the actual buffer size. Consequently, an attacker can send a POST body larger than 2 MiB, causing up to ~8 MiB of attacker‑controlled data to overflow the heap buffer. This overflow occurs before the HTTP basic‑authentication check, meaning no credentials are required.
The vulnerability is reachable only on verto profiles that have at least one `<vhost>, the HTTP request handler is not wired up. The default Verto profile in `verto.conf.xml` does not define `
The impact is severe: heap corruption with fully attacker‑controlled bytes, trivial denial‑of‑service, potential information disclosure (if adjacent allocations are corrupted and later reflected in HTTP responses or WebSocket frames), and plausible remote code execution given the large overflow and complete control over its content. The CVSS 3.1 score is 9.8 (CRITICAL) with vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
The flaw was discovered by security researcher Adam Bedard and patched in FreeSWITCH version 1.11.1, released on 26 May 2026. The fix changes the buffer allocation to match the actual Content‑Length (plus one trailing NUL), ensuring the read loop’s natural termination aligns with the allocation.
DailyCVE Form:
- Platform: FreeSWITCH
- Version: ≤1.11.0
- Vulnerability: Heap overflow
- Severity: CRITICAL 9.8
- date: 2026‑06‑09
- Prediction: Patch 2026‑05‑26
What Undercode Say:
Check FreeSWITCH version
freeswitch -version
Detect vulnerable mod_verto configuration
grep -A5 '<vhost>' /etc/freeswitch/autoload_configs/verto.conf.xml
Reproduce overflow (send >2MiB POST body to /verto)
curl -X POST http://target:8081/verto \
-H "Content-Type: application/x-www-form-urlencoded" \
-H "Content-Length: 10485759" \
--data-binary @/dev/zero
Trigger crash with large body (Python)
python3 -c "import requests; data='A'810241024; requests.post('http://target:8081/verto', data=data, headers={'Content-Length':'8388608'})"
Exploit:
An unauthenticated attacker sends a single HTTP POST request to the verto listener (/verto endpoint) with a Content‑Length header set to ~10 MiB and a body of arbitrary bytes (e.g., all ‘A’). The handler reads up to 10 MiB into a 2 MiB buffer, corrupting heap metadata and adjacent allocations. This can crash the process instantly or, with carefully crafted data, achieve remote code execution.
Protection:
- Upgrade FreeSWITCH to version 1.11.1 or later.
- Remove all `
` blocks from the Verto profile to disable the HTTP handler. - Restrict network access to verto listeners (port 8081/8082) to trusted sources only.
- Disable `mod_verto` entirely if not required.
Impact:
- Heap corruption with attacker‑controlled bytes (up to 8 MiB).
- Reliable denial‑of‑service (crash or hang).
- Possible information disclosure via corrupting adjacent allocations reflected in responses.
- Plausible remote code execution due to large overflow and full control over overwritten data.
🎯Let’s Practice Exploiting & Learn Patching For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
