Summary
Echo: Encoded slash (%2F) bypasses route-level protection and exposes static files
Echo's router and static file handler disagree on URL path decoding. The router matches routes using the raw encoded path (preserving %2F as-is), while StaticDirectoryHandler unescapes %2F to / before resolving filesystem paths. This allows an attacker to bypass route-level access controls and read static files without authorization.
Details
Root cause 1, router.go lines 798-802:
The router uses req.URL.RawPath for route matching when useEscapedPathForRouting is false (the default). This means /admin%2Fsecret.txt is treated as a single path segment and does NOT match the /admin/* route pattern.
if !r.useEscapedPathForRouting && req.URL.RawPath != "" {
path = req.URL.RawPath
}
Root cause 2, echo.go lines 559-568:StaticDirectoryHandler calls url.PathUnescape() on the path parameter before opening files. This converts %2F back to /, resolving admin/secret.txt on disk.
if !disablePathUnescaping {
tmpPath, err := url.PathUnescape(p)
p = tmpPath
}
name := filepath.ToSlash(filepath.Clean(strings.TrimPrefix(p, "/")))
PoC (Screenshot)
Sample:
403:
Bypass with encoded slash:
Impact
Unauthorized static file disclosure. Applications that protect route prefixes with authentication middleware while also serving static files from a broader root are vulnerable. An attacker only needs to encode the slash (/ → %2F) in the URL to bypass all route-level protection.
Common affected pattern:
adminGroup := e.Group("/admin", authMiddleware)
e.StaticFS("/", os.DirFS("public"))
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-55677 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.2.0, 4.15.3); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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github.com/labstack/echo/v5 to 5.2.0 or later; github.com/labstack/echo/v4 to 4.15.3 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-55677? CVE-2026-55677 is a high-severity path traversal vulnerability in github.com/labstack/echo/v5 (go), affecting versions < 5.2.0. It is fixed in 5.2.0, 4.15.3. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-55677? CVE-2026-55677 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which packages are affected by CVE-2026-55677?
github.com/labstack/echo/v5(go) (versions < 5.2.0)github.com/labstack/echo/v4(go) (versions < 4.15.3)github.com/labstack/echo(go) (versions <= 3.3.10)
- Is there a fix for CVE-2026-55677? Yes. CVE-2026-55677 is fixed in 5.2.0, 4.15.3. Upgrade to this version or later.
- Is CVE-2026-55677 exploitable, and should I be worried? Whether CVE-2026-55677 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-55677 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-55677?
- Upgrade
github.com/labstack/echo/v5to 5.2.0 or later - Upgrade
github.com/labstack/echo/v4to 4.15.3 or later
- Upgrade