### Summary `ujson.dumps()` (or `ujson.dump()` or `ujson.encode()`) have a `reject_bytes=False` option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. ### Details The expected behavior is that for `x` being any bytes string, `x == ujson.loads(ujson.dumps(x, reject_bytes=False)).encode(errors="surrogatepass")` should always either be true or `ujson.dumps()` will throw an exception. In reality, some strings which should've been errors are silently rewritten as other strings: * Invalid continuation bytes are replaced with valid ones: `b'\xcf\x13'` -> `b'\xcf\x93'` * Unterminated sequence completes the sequence: `b'\xc3'` -> `b'\xc3\x80'` * ... or leads to reading past the end of string: `b'\xf0\x90\x94'` -> `b"\xf0\x90\x94\x80inxcontrib'"` ### Impact An application relying on reject_bytes=False for UTF-8 handling may experience: - Data integrity issues - Experience validation bypass if said validation occurs before serialisation ### Remediation The missing/broken UTF-8 validation checks were added/fixed in https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf. We recommend upgrading to [UltraJSON 5.13.0](https://github.com/ultrajson/ultrajson/releases/tag/5.13.0). ### Workarounds Decoding bytes to strings in Python before passing them to `ujson.dumps()` avoids this issue.
### Summary `ujson.dumps()` (or `ujson.dump()` or `ujson.encode()`) have a `reject_bytes=False` option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. ### Details The expected behavior is that for `x` being any bytes string, `x == ujson.loads(ujson.dumps(x, reject_bytes=False)).encode(errors="surrogatepass")` should always either be true or `ujson.dumps()` will throw an exception. In reality, some strings which should've been errors are silently rewritten as other strings: * Invalid continuation bytes are replaced with valid ones: `b'\xcf\x13'` -> `b'\xcf\x93'` * Unterminated sequence completes the sequence: `b'\xc3'` -> `b'\xc3\x80'` * ... or leads to reading past the end of string: `b'\xf0\x90\x94'` -> `b"\xf0\x90\x94\x80inxcontrib'"` ### Impact An application relying on reject_bytes=False for UTF-8 handling may experience: - Data integrity issues - Experience validation bypass if said validation occurs before serialisation ### Remediation The missing/broken UTF-8 validation checks were added/fixed in https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf. We recommend upgrading to [UltraJSON 5.13.0](https://github.com/ultrajson/ultrajson/releases/tag/5.13.0). ### Workarounds Decoding bytes to strings in Python before passing them to `ujson.dumps()` avoids this issue.
Update ujson to 5.13.0 if you use the affected versions. Test the change in a non-production environment first.
Local check
hol-guard supply-chain scanUltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps() affects ujson (pip). Severity is medium. ### Summary `ujson.dumps()` (or `ujson.dump()` or `ujson.encode()`) have a `reject_bytes=False` option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. ### Details The expected behavior is that for `x` being any bytes string, `x == ujson.loads(ujson.dumps(x, reject_bytes=False)).encode(errors="surrogatepass")` should always either be true or `ujson.dumps()` will throw an exception. In reality, some strings which should've been errors are silently rewritten as other strings: * Invalid continuation bytes are replaced with valid ones: `b'\xcf\x13'` -> `b'\xcf\x93'` * Unterminated sequence completes the sequence: `b'\xc3'` -> `b'\xc3\x80'` * ... or leads to reading past the end of string: `b'\xf0\x90\x94'` -> `b"\xf0\x90\x94\x80inxcontrib'"` ### Impact An application relying on reject_bytes=False for UTF-8 handling may experience: - Data integrity issues - Experience validation bypass if said validation occurs before serialisation ### Remediation The missing/broken UTF-8 validation checks were added/fixed in https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf. We recommend upgrading to [UltraJSON 5.13.0](https://github.com/ultrajson/ultrajson/releases/tag/5.13.0). ### Workarounds Decoding bytes to strings in Python before passing them to `ujson.dumps()` avoids this issue.
AI coding agents often install or upgrade packages automatically in pip. A medium vulnerability in a dependency can be pulled into a project through a normal install or update without a human reviewing the change, expanding the blast radius from a single package to every agent workspace that depends on it.
| Package | Affected range | Fixed version |
|---|---|---|
| ujsonpip | <=5.12.1 | 5.13.0 |
Fixed versions are reported by the source feed; confirm compatibility before updating.
Reported by GitHub Security Advisories (ghsa).
HOL Guard can help your team review package activity against supported protection paths.
Explore HOL GuardUpdate ujson to 5.13.0 if you use the affected versions. Test the change in a non-production environment first.
Local check
hol-guard supply-chain scanUltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps() affects ujson (pip). Severity is medium. ### Summary `ujson.dumps()` (or `ujson.dump()` or `ujson.encode()`) have a `reject_bytes=False` option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. ### Details The expected behavior is that for `x` being any bytes string, `x == ujson.loads(ujson.dumps(x, reject_bytes=False)).encode(errors="surrogatepass")` should always either be true or `ujson.dumps()` will throw an exception. In reality, some strings which should've been errors are silently rewritten as other strings: * Invalid continuation bytes are replaced with valid ones: `b'\xcf\x13'` -> `b'\xcf\x93'` * Unterminated sequence completes the sequence: `b'\xc3'` -> `b'\xc3\x80'` * ... or leads to reading past the end of string: `b'\xf0\x90\x94'` -> `b"\xf0\x90\x94\x80inxcontrib'"` ### Impact An application relying on reject_bytes=False for UTF-8 handling may experience: - Data integrity issues - Experience validation bypass if said validation occurs before serialisation ### Remediation The missing/broken UTF-8 validation checks were added/fixed in https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf. We recommend upgrading to [UltraJSON 5.13.0](https://github.com/ultrajson/ultrajson/releases/tag/5.13.0). ### Workarounds Decoding bytes to strings in Python before passing them to `ujson.dumps()` avoids this issue.
AI coding agents often install or upgrade packages automatically in pip. A medium vulnerability in a dependency can be pulled into a project through a normal install or update without a human reviewing the change, expanding the blast radius from a single package to every agent workspace that depends on it.
| Package | Affected range | Fixed version |
|---|---|---|
| ujsonpip | <=5.12.1 | 5.13.0 |
Fixed versions are reported by the source feed; confirm compatibility before updating.
Reported by GitHub Security Advisories (ghsa).
HOL Guard can help your team review package activity against supported protection paths.
Explore HOL Guard