CVE-2026-49840: CWE-20: Improper Input Validation in signalwire freeswitch
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.
AI Analysis
Technical Summary
CVE-2026-49840 affects FreeSWITCH, a software-defined telecom stack. The vulnerability arises because esl_recv_event() uses atol() to parse the Content-Length header and directly passes the result to malloc(len + 1) without validating the sign or magnitude of the length. A malicious or man-in-the-middle ESL peer can send a frame with a negative Content-Length, causing heap corruption or crashing any process linked against libesl before authentication. This heap corruption is due to improper input validation (CWE-20), leading to out-of-bounds memory allocation (CWE-122, CWE-787) and signedness issues (CWE-195). The vulnerability has a CVSS 3.1 score of 9.1 (critical) and is patched in FreeSWITCH version 1.11.1.
Potential Impact
An attacker can cause heap corruption or crash processes linked against libesl by sending a malicious ESL frame with a negative Content-Length value. This occurs before client authentication, potentially allowing denial of service or destabilization of the affected system. There is no indication of confidentiality or availability impact beyond process crash and heap corruption. No known exploits are reported in the wild.
Mitigation Recommendations
Upgrade FreeSWITCH to version 1.11.1 or later, where this vulnerability is patched. Patch status is confirmed by the vendor advisory indicating the fix in 1.11.1. No other mitigations are specified or required.
CVE-2026-49840: CWE-20: Improper Input Validation in signalwire freeswitch
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 v3.1
Score 9.1critical
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-49840 affects FreeSWITCH, a software-defined telecom stack. The vulnerability arises because esl_recv_event() uses atol() to parse the Content-Length header and directly passes the result to malloc(len + 1) without validating the sign or magnitude of the length. A malicious or man-in-the-middle ESL peer can send a frame with a negative Content-Length, causing heap corruption or crashing any process linked against libesl before authentication. This heap corruption is due to improper input validation (CWE-20), leading to out-of-bounds memory allocation (CWE-122, CWE-787) and signedness issues (CWE-195). The vulnerability has a CVSS 3.1 score of 9.1 (critical) and is patched in FreeSWITCH version 1.11.1.
Potential Impact
An attacker can cause heap corruption or crash processes linked against libesl by sending a malicious ESL frame with a negative Content-Length value. This occurs before client authentication, potentially allowing denial of service or destabilization of the affected system. There is no indication of confidentiality or availability impact beyond process crash and heap corruption. No known exploits are reported in the wild.
Mitigation Recommendations
Upgrade FreeSWITCH to version 1.11.1 or later, where this vulnerability is patched. Patch status is confirmed by the vendor advisory indicating the fix in 1.11.1. No other mitigations are specified or required.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-01T18:50:36.056Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a283e9b8dd33fbd8553f491
Added to database: 6/9/2026, 4:26:03 PM
Last enriched: 6/9/2026, 4:40:55 PM
Last updated: 6/10/2026, 6:12:17 AM
Views: 7
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