GHSA/SYNC: 1 brand new advisory

Author: jasnow

gems/rdiscount/CVE-2026-35201.yml

@@ -0,0 +1,125 @@
+---
+gem: rdiscount
+cve: 2026-35201
+ghsa: 6r34-94wq-jhrc
+url: https://github.com/davidfstr/rdiscount/security/advisories/GHSA-6r34-94wq-jhrc
+title: rdiscount has an Out-of-bounds Read
+date: 2026-04-06
+description: |
+  ### Summary
+
+  A signed length truncation bug causes an out-of-bounds read in the
+  default Markdown parse path. Inputs larger than `INT_MAX` are truncated
+  to a signed `int` before entering the native parser, allowing the
+  parser to read past the end of the supplied buffer and crash the process.
+
+  ### Details
+
+  In both  public entry points:
+
+  - `ext/rdiscount.c:97`
+  - `ext/rdiscount.c:136`
+
+  `RSTRING_LEN(text)` is passed directly into `mkd_string()`:
+
+  ```c
+  MMIOT *doc = mkd_string(RSTRING_PTR(text),
+  RSTRING_LEN(text), flags);
+  ```
+
+  `mkd_string()` accepts `int len`:
+
+  - `ext/mkdio.c:174`
+
+  ```c
+  Document
+  * mkd_string(const char *buf, int len, mkd_flag_t flags)
+  {
+      struct string_stream about;
+
+      about.data = buf;
+      about.size = len;
+
+      return populate((getc_func)__mkd_io_strget, &about, flags & INPUT_MASK);
+  }
+  ```
+
+  The parser stores the remaining input length in a signed `int`:
+
+  - `ext/markdown.h:205`
+
+  ```c
+  struct string_stream {
+      const
+  char *data;
+      int   size;
+  };
+  ```
+
+  The read loop stops only when `size == 0`:
+
+  - `ext/mkdio.c:161`
+
+  ```c
+  int __mkd_io_strget(struct string_stream *in)
+  {
+      if ( !in->size ) return EOF;
+
+      --(in->size);
+
+      return *(in->data)++;
+  }
+  ```
+
+  If the Ruby string length exceeds `INT_MAX`, the value can truncate
+  to a negative `int`. In that state, the parser continues incrementing
+  `data` and reading past the end of the original Ruby string, causing
+  an out-of-bounds read and native crash.
+
+  Affected APIs:
+
+  - `RDiscount.new(input).to_html`
+  - `RDiscount.new(input).toc_content`
+
+  ### Impact
+
+  This is an out-of-bounds read with the main issue being reliable
+  denial-of-service. Impacted is limited to deployments parses
+  attacker-controlled Markdown and permits multi-GB inputs.
+
+  ### Fix
+
+  just add a checked length guard before the `mkd_string()`
+  call in both public entry points:
+
+  - `ext/rdiscount.c:97`
+  - `ext/rdiscount.c:136`
+  ex:
+
+  ```c
+  VALUE text = rb_funcall(self, rb_intern(\"text\"), 0);
+  long text_len = RSTRING_LEN(text);
+  VALUE buf = rb_str_buf_new(1024);
+  Check_Type(text, T_STRING);
+
+  if (text_len > INT_MAX) {
+      rb_raise(rb_eArgError, \"markdown input too large\");
+  }
+
+  MMIOT *doc = mkd_string(RSTRING_PTR(text), (int)text_len, flags);
+  ```
+
+  The same guard should be applied in `rb_rdiscount_toc_content()`
+  before its `mkd_string()` call.
+cvss_v3: 5.9
+unaffected_versions:
+  - "< 1.3.1.1"
+patched_versions:
+  - ">= 2.2.7.4"
+related:
+  url:
+    - https://nvd.nist.gov/vuln/detail/CVE-2026-35201
+    - https://github.com/davidfstr/rdiscount/security/advisories/GHSA-6r34-94wq-jhrc
+    - http://github.com/davidfstr/rdiscount/releases/tag/2.2.7.4
+    - https://github.com/davidfstr/rdiscount/commit/b1a16445e92e0d12c07594dedcdc56f80b317761
+    - https://github.com/advisories/GHSA-6r34-94wq-jhrc