Buffer overflow in Freeswitch
CVE-2026-49840
FreeSWITCH is a Software Defined Telecom Stack enabling the digital transformation from proprietary telecom switches to a software implementation that runs on any commodity hardware. Prior to version 1.11.1, esl_recv_event() parses Content-Length with atol() and passes the result straight to malloc(len + 1) with no sign or magnitude check. A malicious or man-in-the-middle ESL peer can send a frame with a negative Content-Length to corrupt the heap of, or crash, any process linked against libesl, before the client has authenticated to that peer. This issue has been patched in version 1.11.1.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H.
EPSS exploit prediction
EPSS: 0.005 (39.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 39th percentile — 39.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002
Affected products
- Freeswitch
- Signalwire Freeswitch — versions < 1.11.1
Weakness classification (CWE)
References
- github.com/signalwire/freeswitch/releases/tag/v1.11.1 (Release Notes)
- github.com/signalwire/freeswitch/security/advisories/GHSA-g597-9fgg-ghg9 (Third Party Advisory)
Frequently asked questions
- What is CVE-2026-49840?
- CVE-2026-49840 is a critical-severity vulnerability in Freeswitch, classified under Improper Input Validation. CVSS score: 9.1/10. Published 2026-06-09.
- How severe is CVE-2026-49840?
- Critical severity. CVSS v3 base score is 9.1 out of 10.