Eclipse Jetty: Path parameter traversal

Description (as reported)

Summary

In Jetty 12.1.8, org.eclipse.jetty.util.URIUtil.canonicalPath() may leave dot-dot path segments unnormalized when a semicolon path parameter marker is followed by a slash and a dot segment.

A minimal example is:

/public;/../admin/secret

In my local reproduction, URIUtil.canonicalPath() returns:

/public/../admin/secret

instead of the expected normalized path:

/admin/secret

When Jetty's SecurityHandler.PathMapped is used to protect a path prefix such as /admin/*, the non-normalized canonical path may not match the protected prefix. As a result, an unauthenticated request may bypass the configured path-based security constraint.

Tested Version

Jetty: 12.1.8 JDK: 17.0.18 Maven: 3.9.14

Maven artifacts used:

org.eclipse.jetty:jetty-server:12.1.8 org.eclipse.jetty:jetty-security:12.1.8 org.eclipse.jetty:jetty-session:12.1.8

Only confirmed Jetty 12.1.8 so far.

Minimal Reproduction

Starts a minimal Jetty server with the following security setup:

SecurityHandler.PathMapped security = new SecurityHandler.PathMapped();
security.put("/admin/*", Constraint.from("admin"));
security.put("/*", Constraint.ALLOWED);
security.setAuthenticator(new BasicAuthenticator());

The test then sends requests with no Authorization header.

Observed result:

GET /admin/secret                  -> 401
GET /public;x/../admin/secret      -> 200

The handler receives paths such as:

/public/../admin/secret

This suggests that the /admin/* security constraint is bypassed because PathMapped matching is performed against the non-normalized canonical path.

Suspected Root Cause

The suspected root cause is in URIUtil.canonicalPath().

The relevant logic is approximately:

    for (int i = 0; i < end; i++)
    {
        char c = encodedPath.charAt(i);

        switch (c)
        {
            case ';':
                if (builder == null)
                {
                    builder = new Utf8StringBuilder(encodedPath.length());
                    builder.append(encodedPath, 0, i);
                }

                while (++i < end)
                {
                    if (encodedPath.charAt(i) == '/')
                    {
                        builder.append('/');
                        break;
                    }
                }
                break;

            case '.':
                if (slash)
                    normal = false;
                if (builder != null)
                    builder.append(c);
                break;
        }

        slash = c == '/';
    }

    String canonical = (builder != null)
        ? (onBadUtf8 == null ? builder.toCompleteString() : builder.takeCompleteString(onBadUtf8))
        : encodedPath;
    return normal ? canonical : normalizePath(canonical);

For the input:

/public;/../admin/secret

when the outer loop reaches the semicolon:

    i      = 7
    c      = ';'
    slash  = false
    normal = true

Inside case ';', the while (++i < end) loop advances i to the next character, which is already '/' for the empty path parameter form ";/".

The code then appends '/' to the canonical builder:

builder.append('/');

At this point, the canonical builder ends with '/':

/public/

However, the local variable c is still the old value ';', because c was read before entering the switch and is not updated when the inner loop advances i.

After leaving the switch, the loop updates the slash state using:

slash = c == '/';

Since c is still ';', slash becomes false.

On the next iteration, the scanner reaches '.', which is the first dot in the following "../" segment. Because slash is incorrectly false, this code does not run:

    if (slash)
        normal = false;

Therefore normal remains true, and canonicalPath() returns the canonical string directly instead of calling normalizePath(canonical).

The result is:

/public/../admin/secret

instead of:

/admin/secret

In short:

case ';' advances the scan position i and appends '/' to the canonical builder, but the loop tail still updates slash from the stale character c=';'. As a result, the following dot-dot segment is not detected as a path traversal segment.

More Precise Trigger Condition

The issue is not limited to a non-empty path parameter such as ";x".

The more precise trigger shape is:

;[^/]*/.

Examples:

    /public;/../admin/secret
    /public;x/../admin/secret
    /public;anything/../admin/secret
    /public;/./admin/secret

The minimal form is:

/public;/../admin/secret

because the semicolon is immediately followed by '/', so the inner while loop reaches '/' on its first increment.

Potential Minimal Fix Direction

A minimal fix would be to ensure that, when case ';' consumes input until '/' and appends '/' to the canonical builder, the slash state reflects the last effective character in the canonical path.

For example, conceptually:

    case ';':
        if (builder == null)
        {
            builder = new Utf8StringBuilder(encodedPath.length());
            builder.append(encodedPath, 0, i);
        }

        while (++i < end)
        {
            if (encodedPath.charAt(i) == '/')
            {
                builder.append('/');
                slash = true;
                break;
            }
        }
        continue;

The important part is to avoid the loop tail from overwriting slash using the stale c value:

slash = c == '/';

In other words, slash should represent the last effective character appended to the canonical builder, not the original input character read before case ';' advanced i.