GHSA-7FQQ-Q52P-2JJG

OpenCC versions before 1.2.0 contain two CWE-125: Out-of-bounds Read issues caused by length validation failures in UTF-8 processing. When handling malformed or truncated UTF-8 input, OpenCC trusted derived length values without enforcing the invariant that processed length must not exceed the remaining input buffer. This could result in out-of-bounds reads during segmentation or conversion.

Details

Two independent code paths in OpenCC failed to enforce the invariant:

matchedLength <= remainingLength

Both paths assumed derived length values were valid and within input bounds, but did not validate that assumption against the remaining buffer. This created the following failure chain:

invalid UTF-8 -> incorrect derived length -> incorrect pointer advance -> remaining-length desynchronization -> out-of-bounds read

In MaxMatchSegmentation::Segment, this could desynchronize remaining-length tracking and cause out-of-bounds reads during prefix matching.

In Conversion::Convert(const char*), similar logic could advance processing past the end of the input string and read beyond the null terminator into adjacent memory. In some cases, unintended heap bytes could be propagated into the conversion result.

PR #1005 fixes both issues by explicitly tracking input boundaries, recomputing remaining length on each iteration, and clamping processed lengths so the buffer-bound invariant is preserved.

Affected versions:

• All versions before 1.2.0

Patched version:

• 1.2.0

PoC

Build a vulnerable version with AddressSanitizer enabled and process input ending with a truncated UTF-8 sequence, such as a missing final byte of a 3-byte character. The original report and ASan reproduction are available in Issue #997.

Credit

OpenCC thanks @oneafter for reporting the issue.

This vulnerability may cause process crashes and limited, non-deterministic information disclosure when OpenCC processes malformed or attacker-controlled UTF-8 input. The issue does not indicate arbitrary write or code execution.

OpenCC is distributed through system and language-specific package managers, prebuilt binaries, container images, and downstream software, so affected versions may be present even when it is not listed as a direct dependency. Users should upgrade all installed or bundled copies of OpenCC to 1.2.0 or later.

A read operation accesses a memory location beyond the intended buffer boundary. Typical impact: sensitive data disclosure or crash.

GHSA-7FQQ-Q52P-2JJG has a CVSS score of 6.5 (Medium). 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 (1.2.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is GHSA-7FQQ-Q52P-2JJG? GHSA-7FQQ-Q52P-2JJG is a medium-severity out-of-bounds read vulnerability in opencc (npm), affecting versions < 1.2.0. It is fixed in 1.2.0. A read operation accesses a memory location beyond the intended buffer boundary.
2. How severe is GHSA-7FQQ-Q52P-2JJG? GHSA-7FQQ-Q52P-2JJG has a CVSS score of 6.5 (Medium). 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.
3. Which packages are affected by GHSA-7FQQ-Q52P-2JJG?
   • opencc (npm) (versions < 1.2.0)
   • OpenCC (pip) (versions < 1.2.0)
4. Is there a fix for GHSA-7FQQ-Q52P-2JJG? Yes. GHSA-7FQQ-Q52P-2JJG is fixed in 1.2.0. Upgrade to this version or later.
5. Is GHSA-7FQQ-Q52P-2JJG exploitable, and should I be worried? Whether GHSA-7FQQ-Q52P-2JJG 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
6. What actually determines whether GHSA-7FQQ-Q52P-2JJG 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.
7. How do I fix GHSA-7FQQ-Q52P-2JJG?
   • Upgrade opencc to 1.2.0 or later
   • Upgrade OpenCC to 1.2.0 or later