CVE-2026-49840
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.31%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 9.1 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
- EPSS
- 0.31% probability · 24th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-20, CWE-122, CWE-195, CWE-787
- Affected
- freeswitch/freeswitch
- Source
- security-advisories@github.com
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.