CVE-2026-88359: Libfyaml libfyaml vulnerability
libfyaml 0.9.6 contains a stack exhaustion vulnerability in fyatomiterformat(). When processing a specially crafted YAML document containing a very large literal or folded block scalar, the function repeatedly grows an internal buffer using alloca() inside a loop. The allocated stack memory is not released until the function returns, causing cumulative stack growth that can exceed the process stack limit and result in SIGSEGV and denial of service.
Affected Software
Event History
Frequently Asked Questions
What input is required to trigger the denial of service?
An attacker must cause libfyaml to process a specially crafted YAML document with a very large literal or folded block scalar. Processing that input can cumulatively exhaust the process stack and terminate the process with SIGSEGV.
Which deployments are exposed?
Deployments using libfyaml 0.9.6 are affected when they parse YAML documents that may contain attacker-controlled or otherwise untrusted large block scalars.
How can I tell whether an incident may be related to this issue?
Look for processes using libfyaml that crash with SIGSEGV while parsing YAML containing unusually large literal or folded block scalar content. The failure results from stack growth in fy_atom_iter_format().