CVE-2026-49840
Heap corruption via negative Content-Length in esl_recv_event() can crash FreeSWITCH before auth.
Is CVE-2026-49840 being exploited?
Not confirmed. CVE-2026-49840 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.31% probability of exploitation in the next 30 days.
How severe is CVE-2026-49840?
CVE-2026-49840 is rated Critical with a CVSS score of 9.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-49840?
Yes. A fix has been recorded for CVE-2026-49840. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-49840 affect?
CVE-2026-49840 affects FreeSWITCH < 1.11.1, libesl (ESL library). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-49840?
Upgrade to FreeSWITCH 1.11.1 or newer
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote DoS via heap corruption/crash in libesl; MITM frame with negative Content-Length before authentication.
Immediate action required
- affected< 1.11.1
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.