CVE-2026-116574: FreeSWITCH: Off-by-one heap write in core XML serialization of four-byte UTF-8 sequences

Vulnerability summary

CVE-2026-116574 is a medium (CVSS 5.9) Off-by-one Error vulnerability in signalwire freeswitch. EPSS estimates a 0.38% chance of exploitation in the next 30 days, higher than 32.1% of scored vulnerabilities.

Timeline

1. 05-11-2026
   PublishedVulnerability first disclosed.
2. 09-11-2026
   Last modifiedVulnerability information updated.

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 1.11.2, switch_xml_ampencode() reserved only ten bytes for the widest numeric character reference produced from a four-byte UTF-8 sequence, omitting space for the terminating NUL. When remote-supplied text was serialized at the exact buffer-growth boundary, the terminator wrote one byte beyond the heap allocation. Reachable surfaces include mod_xml_cdr, conference and formatted CDR XML, XML Event Socket output, and XML API output that serializes caller-controlled values. The fixed zero-byte write can abort the process or truncate an adjacent object, while remote code execution has not been demonstrated. This issue is fixed in version 1.11.2.

• CWE-193Off-by-one ErrorA product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.