Updated advisory posts against rubysec/ruby-advisory-db@3b738da

Author: flavorjones

advisories/_posts/2026-04-06-CVE-2026-35201.md

@@ -0,0 +1,132 @@
+---
+layout: advisory
+title: 'CVE-2026-35201 (rdiscount): rdiscount has an Out-of-bounds Read'
+comments: false
+categories:
+- rdiscount
+advisory:
+  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
+---