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web: reject malformed percent escapes in URLs - #24248
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url_percent_escape_decode() decoded the two characters after any byte with from_hex(), which maps every character to a number. UTF-8 continuation triplets were not required to start with '%' and non-hex digits produced arbitrary bytes, so "%C3xA9" decoded to "é" and "%zz" to "3". Require '%' followed by two ASCII hex digits. Callers already treat a zero result as failure. Add url_unittest() to -W unittest.
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title clearly and concisely describes the main change: rejecting malformed percent escapes in web URLs. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
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All reported issues were addressed across 2 files
Architecture diagram
sequenceDiagram
participant App as Netdata Daemon (main.c)
participant URL as URL Decoder (url.c)
participant Decoder as url_percent_escape_decode()
participant Caller as URL Callers (Web Server)
participant Test as Unit Test Harness
Note over App,Test: URL Percent Escape Decoding Flow
App->>App: netdata_main() starts
App->>URL: url_decode_r() called (runtime)
URL->>Decoder: Process each character sequence
Decoder->>Decoder: Check s[0] == '%' AND hex digit checks
alt Valid escape (%XX where X is hex)
Decoder->>Decoder: Decode byte from hex digits
Decoder-->>URL: Return decoded byte
else Invalid format (no %, non-hex, truncated)
Decoder-->>URL: Return 0 (failure)
end
URL->>URL: Build decoded output buffer
alt Decode failure
URL-->>Caller: Return NULL / failure indicator
Caller->>Caller: Handle failed decode (existing logic)
else Decode success
URL-->>Caller: Return decoded URL string
Caller->>Caller: Route based on decoded URL
end
Note over App,Test: Unit Test Flow (-W unittest)
App->>App: Execute unittest suite
App->>Test: Invoke url_unittest()
Test->>Test: Run 13 test cases
Test->>URL: Test URL decoding (valid escapes, '+', UTF-8)
Test->>URL: Test URL decoding (malformed inputs)
URL-->>Test: Success/failure per test case
Test->>Test: Compare results against expectations
alt All tests pass
Test-->>App: Return 0 (success)
else Test failures detected
Test-->>App: Return error count (non-zero)
end
App->>App: Continue startup or abort based on test results
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Actionable comments posted: 1
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Inline comments:
Review comments at @src/libnetdata/url/url.c:
- Line 69: Check the return value of url_decode_r() in the web client’s path and
query decoding flow, and reject the request before routing if either decode
fails. Only append decoded data after successful decoding so malformed escapes
cannot route using a partial URL.
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src/daemon/main.csrc/libnetdata/url/url.c
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web_client_decode_path_and_query_string() ignored url_decode_r() failures and dispatched the decoded prefix, so /api/v1/info%zz was served as /api/v1/info. Return HTTP_VALIDATION_MALFORMED_URL (400) for any decode failure, including invalid UTF-8 and stream requests, and keep 414 for oversized URLs; the WebRTC caller maps both. The ACLK proxy credential parser now treats a decode failure like a missing separator instead of using a truncated username or password.
stelfrag
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All reported issues were addressed across 5 files (changes from recent commits).
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The malformed URL cases ran with no request mode, so the stream branch of web_client_decode_path_and_query_string() was not exercised.
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stelfrag
marked this pull request as ready for review
October 12, 2026 10:27
thiagoftsm
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Oct 14, 2026
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Netdata rejected malformed URL as expected. LGTM!
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Nov 4, 2026
* libnetdata: validate percent escapes when decoding URLs url_percent_escape_decode() decoded the two characters after any byte with from_hex(), which maps every character to a number. UTF-8 continuation triplets were not required to start with '%' and non-hex digits produced arbitrary bytes, so "%C3xA9" decoded to "é" and "%zz" to "3". Require '%' followed by two ASCII hex digits. Callers already treat a zero result as failure. Add url_unittest() to -W unittest. * web: reject URLs that fail to decode web_client_decode_path_and_query_string() ignored url_decode_r() failures and dispatched the decoded prefix, so /api/v1/info%zz was served as /api/v1/info. Return HTTP_VALIDATION_MALFORMED_URL (400) for any decode failure, including invalid UTF-8 and stream requests, and keep 414 for oversized URLs; the WebRTC caller maps both. The ACLK proxy credential parser now treats a decode failure like a missing separator instead of using a truncated username or password. * web: cover malformed stream requests in the decode unittest The malformed URL cases ran with no request mode, so the stream branch of web_client_decode_path_and_query_string() was not exercised. (cherry picked from commit 3065514)
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Two problems with malformed percent escapes in URLs:
url_percent_escape_decode()decoded the two characters after any byte withfrom_hex(), which maps every character to a number. UTF-8 continuation triplets were not required to start with%, and non-hex digits produced arbitrary bytes:%C3xA9decoded toé,%zzto3. It now requires%followed by two ASCII hex digits.web_client_decode_path_and_query_string()ignoredurl_decode_r()failures and dispatched the decoded prefix, so/api/v1/info%zzwas served as/api/v1/info(and/api/v1/info%00on master). It now returnsHTTP_VALIDATION_MALFORMED_URL(HTTP 400) for any decode failure, including invalid UTF-8 and stream requests; oversized URLs keep 414. The WebRTC caller maps both.The ACLK proxy credential parser now treats a decode failure like a missing separator (logs and connects without authentication) instead of using a truncated username or password.
Tests:
url_unittest()in-W unittest: master fails 2 of 13 cases (%C3xA9,%zz), the fix passes all;web_client_request_size_unittest()now also checks malformed paths/queries; full-W unittestpassesa%20b,%C3%A9, a v3 data query with%5B0%5D) still 200;/api/v1/info%zz,?x=%C3xA9,?x=%C0%AF,?x=%zz,?x=100%,/api/v1/info%00now 400 (master: 404 or 200); a child still streams to the parentwebrtc.ccompiled withHAVE_LIBDATACHANNELagainst libdatachannel v0.20.1 headers (WebRTC is off in default builds)Behavior change: a request with a literal unencoded
%that is not followed by two hex digits (e.g.?x=100%) now gets 400 instead of being served with a truncated URL.Summary by CodeRabbit