In 2022, Intel acknowledged a significant security flaw, tracked as CVE-2022-26369, affecting certain versions of its XMM 756 modem firmware. This out-of-bounds read bug allowed privileged users to possibly escalate their privileges under specific circumstances. This post breaks the vulnerability down in plain English, explores how it arises, and looks at proof-of-concept code, with links to original sources.

What Is CVE-2022-26369?

CVE-2022-26369 is categorized as an out-of-bounds read in the Intel XMM 756 modem software, affecting versions before M2_756_R_01.2146.00. This bug could let nearby privileged attackers (like ones with access over USB, PCIe, or other local channels) read memory they shouldn’t be able to, possibly leading to privilege escalation.

Impact: Potential privilege escalation via adjacent access

- Attack Complexity: Low, but needs privileged/adjacent access

Official Details

- Intel Security Advisory INTEL-SA-00737
- National Vulnerability Database

What is an Out-of-Bounds Read?

Out-of-bounds read means a program tries to read data outside the memory area it should access. This can unintentionally leak sensitive information, or cause the software to act unpredictably.

How Does This Happen in the XMM 756 Modem Software?

Typically, modem firmware runs in a high-privilege context, and should never process invalid data that lets it peek beyond buffer boundaries. In affected versions, certain inputs sent by privileged users (operators, drivers, or perhaps even maliciously crafted data via connected peripherals) could cause the modem to read data out-of-bounds—leaking memory, revealing secrets, and sometimes even setting up for a privilege escalation.

Exploit Details

While Intel hasn’t published full details for security reasons, the advisory hints at the type of coding mistake:

Imagine the firmware has C code like this

#define BUFFER_SIZE 64

void process_incoming_data(uint8_t *src, size_t len) {
    uint8_t buffer[BUFFER_SIZE];
    // BAD: len is not checked!
    memcpy(buffer, src, len);
}

If an attacker (with privileged/adjacent access) sends more than 64 bytes, the function copies past the end of buffer, causing out-of-bounds memory access—which could allow reading or even manipulation of sensitive modem data.

Proof of Concept (PoC)

A real-world proof of concept for this bug would require modem hardware, privileged access, and the vulnerable firmware, but the generic steps would look like:

1. Gain Privileged Access: Become a privileged modem user or system operator, or find a driver interface that interacts with the firmware.
2. Craft Malicious Packet: Send a message or command that intentionally contains more data than expected.
3. Trigger Vulnerability: The modem firmware, because of the bug, reads memory outside the allocated buffer.
4. Read Sensitive Data: This memory might contain passwords, configuration data, or code that could be further abused for privilege escalation.

PoC Example (Pseudocode)

// Using a vulnerable interface
allocate buffer of 128 bytes with known pattern
send buffer to modem firmware through test driver
// Modem firmware reads extra data past 64 bytes as per bug
// Leaked modem memory is returned or handled in an unexpected way
// Attacker analyzes leak for secrets

Note: Actual exploitation will vary depending on the modem's configuration and the platform.

Mitigation and Fix

Intel quickly patched this in version M2_756_R_01.2146.00 and later. Users and system integrators should:

Upgrade XMM 756 Modem Firmware: Get firmware updates from your device vendor.

2. Restrict Privileged Access: Only allow trusted users/drivers to interact with modem firmware.

References & Resources

- Intel Security Advisory: INTEL-SA-00737
- CVE-2022-26369 on NVD

Conclusion

CVE-2022-26369 highlights how a simple coding oversight can have major consequences, especially in privileged system components like modem firmware. If you use hardware with Intel XMM 756 modems, check with your vendor that the latest firmware is applied. Always treat privileged access as a critical attack surface, and never assume adjacent devices can’t be security risks.

Timeline

Published on: 11/11/2022 16:15:00 UTC
Last modified on: 11/16/2022 18:09:00 UTC