CVE-2026-49885

Executive Summary

CVE-2026-49885 is an out-of-bounds write vulnerability in the rw_t4t_update_file function of rw_t4t.cc, caused by an integer overflow. The flaw allows a local attacker to corrupt memory and potentially escalate privileges to the level of the affected process, with no additional execution privileges and no user interaction required. The vulnerability is unpatched, has no public proof-of-concept, and has not been observed in CISA KEV; however, its CVSS score of 7.8 (High) reflects significant confidentiality, integrity, and availability impact if successfully exploited.

Technical Analysis

The vulnerability resides in rw_t4t_update_file within rw_t4t.cc. The name and file extension strongly suggest this is part of an NFC (Near Field Communication) or smartcard framework implementing the T4T (Type 4 Tag) specification, likely within an Android or similar mobile/embedded platform. The root cause is an integer overflow (CWE-190). When an integer calculation used for size, offset, or index computation exceeds the representable range of its type, the resulting value wraps or truncates, leading to an incorrectly small buffer size or an out-of-range index. This incorrect value is then used in a write operation, causing data to be written outside the intended buffer boundary — an out-of-bounds write (CWE-787).

The NVD description explicitly states the vulnerability is reachable in rw_t4t_update_file and can lead to local escalation of privilege. The CVSS vector indicates the attack is local (AV:L), requires low complexity (AC:L), requires low privileges (PR:L), and needs no user interaction (UI:N). The impact to confidentiality, integrity, and availability is High across all three categories. This combination suggests a memory corruption primitive that an attacker with the ability to invoke the vulnerable code path — likely through a crafted NFC tag, a local application, or a malicious file processed by the affected component — can use to overwrite adjacent memory structures. In a typical memory-corruption exploitation chain, this could allow hijacking of control flow or modification of security-critical data, resulting in code execution with elevated privileges.

The exact trigger conditions are not detailed in the available data. No specific input format, packet structure, NFC command, or file content is described. Therefore, the precise mechanism by which the integer overflow is induced (e.g., a length field, offset calculation, or arithmetic on attacker-supplied data) cannot be determined from the provided information. The affected version range, vendor, and product names are also unknown, which limits the ability to identify specific vulnerable deployments.

Exploitation Scenarios

No public proof-of-concept or exploit code is available for CVE-2026-49885. The following attack chain is inferred strictly from the vulnerability class (integer overflow leading to out-of-bounds write) and the NVD description. Specific function names, parameters, and code paths are limited to those explicitly stated.

1. Reconnaissance / Target Identification The attacker must first identify a target system that implements the rw_t4t_update_file function — likely a mobile device, embedded NFC controller, or application that processes Type 4 Tag data using the rw_t4t.cc code. Because the vendor and product are unknown, reconnaissance would focus on systems exposing NFC or T4T functionality, such as Android-based devices with NFC enabled or applications that parse T4T-formatted data. The attacker needs only local access (AV:L), which could mean physical proximity for NFC, a malicious app installed on the device, or a local file processed by a vulnerable service.

2. Triggering the Integer Overflow The attacker crafts input that causes an integer overflow within the logic of rw_t4t_update_file. This likely involves supplying a large value in a field that is used to calculate a buffer size, offset, or index. When the arithmetic operation overflows, the computed size or index becomes unexpectedly small or wraps to a value that bypasses bounds checking. The exact input vector is not specified, but it could be a malformed T4T file, an NFC command, or data passed through an API that calls rw_t4t_update_file.

3. Out-of-Bounds Write The overflowed size or index is then used in a memory write operation. Because the computed value is incorrect, the write occurs outside the allocated buffer. This corrupts adjacent memory, which may contain control data, function pointers, or other critical structures. The attacker can potentially influence what data is written and where, depending on the nature of the overflow and the surrounding memory layout.

4. Privilege Escalation and Post-Exploitation With a controlled out-of-bounds write, the attacker may corrupt security-critical data or hijack execution flow to run arbitrary code with the privileges of the vulnerable process. Since the vulnerability leads to "local escalation of privilege," the attacker could gain elevated rights on the device, bypassing application sandboxes or user-level restrictions. No user interaction is required, meaning the attack can proceed silently once the vulnerable code path is reached. Post-exploitation impact could include data theft, persistence, or further compromise of the device and its data, consistent with the High confidentiality, integrity, and availability impacts in the CVSS vector.

Impact Assessment

CVE-2026-49885 carries a CVSS 3.1 base score of 7.8 (High). The vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H indicates:

• Attack Vector (AV:L): The attacker must have local access, which could be physical (e.g., NFC proximity) or logical (e.g., a malicious app or local user account). This limits the attack surface compared to a network-exploitable flaw but is still significant for mobile and embedded devices where local access is often achievable.
• Attack Complexity (AC:L): No special conditions are required beyond reaching the vulnerable function; the attack is straightforward once the vector is identified.
• Privileges Required (PR:L): The attacker needs low-level privileges, such as a normal user or app context, not administrative rights.
• User Interaction (UI:N): No user action is needed, making the exploit silent and automatable.
• Scope (S:U): The impact is confined to the vulnerable component's security authority.
• Confidentiality, Integrity, Availability (C:H/I:H/A:H): All three are rated High, meaning a successful exploit could result in total loss of confidentiality, integrity, and availability for the affected component.

The business impact depends on the deployment context. If the vulnerable code is part of a mobile operating system or a widely used NFC library, the blast radius could include millions of devices. A local privilege escalation in such a context could allow malicious apps to escape sandboxes, access sensitive user data (e.g., credentials, messages, financial information), or persist on the device. For enterprise environments, this could lead to compromised endpoints, lateral movement, and data breaches. Because the vulnerability is unpatched and no vendor fix is available, organizations relying on affected systems face an ongoing risk with no direct remediation.

Detection Guidance

Sigma Rule

title: Potential Exploitation of CVE-2026-49885 - Out-of-Bounds Write in rw_t4t_update_file
id: 7e3f9a2c-1b4d-4e8a-9c7f-2d5a8b6e1f3a
status: experimental
description: Detects potential memory corruption attempts targeting the rw_t4t_update_file function via unusual NFC/T4T data processing or local application behavior.
author: Threat Intelligence
date: 2026-05-12
logsource:
  category: process_creation
  product: android
detection:
  selection_img:
    - Image|endswith: '/app_process'
    - Image|endswith: '/system/bin/app_process'
  selection_cmd:
    - CommandLine|contains: 'rw_t4t'
    - CommandLine|contains: 'nfc'
    - CommandLine|contains: 't4t'
  condition: selection_img and selection_cmd
falsepositives:
  - Legitimate NFC service operations
  - Debugging sessions
level: medium
tags:
  - attack.t1068
  - cve.2026-49885

YARA Rule

rule CVE_2026_49885_Integer_Overflow_rw_t4t
{
    meta:
        description = "Detects code patterns potentially related to integer overflow in rw_t4t_update_file"
        author = "Threat Intelligence"
        date = "2026-05-12"
        reference = "CVE-2026-49885"
        severity = "high"
    strings:
        $func = "rw_t4t_update_file" ascii wide
        $file = "rw_t4t.cc" ascii wide
        $t4t = "T4T" ascii wide
    condition:
        any of ($func, $file) or (all of ($t4t) and filesize < 10MB)
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2026-49885 Potential Exploitation Attempt - Out-of-Bounds Write in rw_t4t_update_file"; flow:to_server,established; content:"rw_t4t"; nocase; content:"update_file"; nocase; distance:0; within:100; classtype:attempted-admin; sid:10000001; rev:1; reference:cve,2026-49885;)

Elastic Detection

process where process.name in ("app_process", "system_server") and
  process.command_line : ("*rw_t4t*" or "*nfc*" or "*t4t*") and
  event.action == "start"

Splunk SPL Query

index=android_logs (source="*nfc*" OR source="*t4t*") 
| search "rw_t4t_update_file" OR "out-of-bounds" OR "integer overflow" 
| stats count by host, source, user, process 
| where count > 0

Wazuh OSSEC Rule

<group name="cve-2026-49885,">
  <rule id="100001" level="10">
    <decoded_as>json</decoded_as>
    <field name="message">rw_t4t_update_file</field>
    <description>CVE-2026-49885: Possible exploitation attempt targeting rw_t4t_update_file</description>
    <mitre>
      <id>T1068</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate Mitigations

   • Disable NFC or T4T functionality on affected devices if not operationally required.
   • Restrict local access to the vulnerable component: enforce application sandboxing, remove unnecessary local user accounts, and limit physical access to devices.
   • Monitor for anomalous memory corruption indicators (e.g., crashes, abnormal process terminations) that could indicate exploitation attempts.
   • Apply runtime application self-protection (RASP) or memory protection mechanisms (e.g., ASLR, DEP) where available to raise the exploitation bar.

2. Patch / Upgrade Steps

   • No official patch is available. Continuously monitor the vendor's security advisories and NVD for updates.
   • Once a patch is released, prioritize upgrading all affected systems, especially mobile devices and embedded NFC components.
   • If the vulnerable code originates from an open-source project, subscribe to its repository for commits referencing CVE-2026-49885 or integer overflow fixes in rw_t4t.cc.

3. Long-Term Hardening

   • Implement secure coding practices: use safe integer arithmetic libraries, validate all input sizes, and perform strict bounds checking before memory writes.
   • Conduct regular code reviews and static analysis focused on integer overflow and out-of-bounds write patterns.
   • Deploy endpoint detection and response (EDR) solutions with memory integrity monitoring to detect and block exploitation attempts.
   • Maintain an inventory of all systems using NFC/T4T stacks and track their patch status.

References

• NVD – CVE-2026-49885: https://nvd.nist.gov/vuln/detail/CVE-2026-49885
• CWE-190: Integer Overflow or Wraparound: https://cwe.mitre.org/data/definitions/190.html
• CWE-787: Out-of-bounds Write: https://cwe.mitre.org/data/definitions/787.html
• MITRE ATT&CK T1068 – Exploitation for Privilege Escalation: https://attack.mitre.org/techniques/T1068/
• CISA Known Exploited Vulnerabilities Catalog (not listed as of report date): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No known threat actor campaigns or exploit-in-the-wild evidence are associated with CVE-2026-49885 at this time.