CVE-2021-25489
Samsung Mobile Devices Improper Input Validation Vulnerability
Description
CVE-2021-25489 is a format string vulnerability in the modem interface driver of Samsung Android devices, caused by missing input validation. Assuming radio permission is gained, an attacker can exploit this format string bug to cause a kernel panic, resulting in a denial of service on the affected Samsung mobile device. The vulnerability was addressed in the Samsung SMR October 2021 Release 1 security update. Despite its low CVSS score of 3.3, CISA has added CVE-2021-25489 to the Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild, likely as part of exploit chains targeting Samsung mobile devices.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:LOpen in CalculatorCWEs
Affected Products
| Vendor | Product | Version |
|---|---|---|
| samsung | android | 8.1; 9.0; 10.0; 11.0 |
Multiple CVSS Assessments
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
References
- https://security.samsungmobile.com/securityUpdate.smsb?year=2021&month=10(Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-25489(US Government Resource)
Weakness Type
CWE-20: Improper Input Validation
In CVE-2021-25489, the Samsung modem interface driver fails to properly validate input data before processing it, allowing specially crafted input to be interpreted as format string specifiers. This lack of input validation in the modem driver permits an attacker to influence how the kernel processes data, leading to a kernel panic.
Learn more: CWE-20 — Improper Input Validation
CWE-134: Use of Externally-Controlled Format String
The modem interface driver in Samsung Android devices uses externally-supplied input directly as a format string argument without sanitization. This format string vulnerability (CWE-134) allows an attacker with radio permission to inject format specifiers that cause the kernel to read from or write to arbitrary memory locations, triggering a kernel panic and denial of service.
Learn more: CWE-134 — Use of Externally-Controlled Format String
Impact Analysis
CVE-2021-25489 carries a CVSS v3.1 score of 3.3 (Low), reflecting its limited direct impact but still warranting attention due to confirmed active exploitation. The vulnerability requires local access with low privileges and has low attack complexity, but it specifically requires that radio permission has been gained as a prerequisite. No user interaction is needed to trigger the exploit. The impact is limited to availability (Low) — the format string bug causes a kernel panic that crashes the device, but no confidentiality or integrity impact is indicated by the CVSS metrics. However, the inclusion in CISA's KEV catalog suggests this vulnerability is being exploited as part of multi-stage attack chains against Samsung devices, where a device crash via kernel panic may serve as a stepping stone or component of a larger exploit sequence that includes CVE-2021-25487, which targets the same modem interface driver.
Exploit Maturity
CISA has confirmed active exploitation of CVE-2021-25489 in the wild by adding it to the Known Exploited Vulnerabilities catalog with a remediation deadline of July 20, 2023. No public proof-of-concept exploit code has been identified in the available references, indicating that exploitation is conducted by sophisticated threat actors using privately developed tools. The EPSS score of 0.36% (58th percentile) suggests limited widespread exploitation, but the KEV catalog inclusion confirms that targeted attacks are occurring, likely in conjunction with CVE-2021-25487 which affects the same Samsung modem interface driver and was added to the KEV catalog on the same date. The ransomware association is listed as unknown.
Remediation
- Apply Samsung security updates immediately as directed by CISA: apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. Samsung addressed this format string vulnerability in the SMR October 2021 Release 1.
- Update all affected Samsung Android devices to the October 2021 or later security patch level by checking Settings > About Phone > Software Information and ensuring the security patch date shows 2021-10-01 or later.
- Enforce mobile device management (MDM) policies to ensure that Samsung devices in the enterprise fleet receive timely security updates. Implement strict input validation policies at the application layer and restrict applications that interact with modem interfaces to limit the attack surface.
- Monitor Samsung devices for kernel panic events and unexpected reboots, which may indicate exploitation attempts targeting the modem interface driver. Correlate these events with other suspicious activity such as privilege escalation attempts associated with CVE-2021-25487.
- Implement defense-in-depth measures for mobile device security, including application sandboxing enforcement and restricting radio-level permissions to only trusted system components, to reduce the likelihood that an attacker can achieve the radio permission prerequisite needed to exploit this format string vulnerability.
Technical Details
CVE-2021-25489 is a format string vulnerability caused by the combination of improper input validation (CWE-20) and the use of an externally-controlled format string (CWE-134) in the Samsung modem interface driver on Android devices. The driver fails to validate or sanitize input data before using it as a format string argument in a string formatting function, allowing an attacker who has gained radio permission to inject format specifiers such as %s, %x, or %n that cause the kernel to access unintended memory locations. The CVSS vector (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L) indicates this is a local attack requiring low privileges with no user interaction needed, though the prerequisite of radio permission limits the exploitability. The two CWE classifications are complementary: CWE-20 describes the root cause (missing input validation in the modem driver), while CWE-134 describes the specific manifestation (externally-controlled format string), and together they result in a kernel panic that crashes the device.
Frequently Asked Questions
Is CVE-2021-25489 being actively exploited?
Yes, CISA has confirmed active exploitation of CVE-2021-25489 by adding it to the Known Exploited Vulnerabilities catalog with a remediation deadline of July 20, 2023. Despite its low CVSS score of 3.3, it is believed to be exploited as part of attack chains targeting Samsung mobile devices, potentially in combination with CVE-2021-25487 which targets the same modem driver component.
What products are affected by CVE-2021-25489?
CVE-2021-25489 affects Samsung Android mobile devices running firmware versions prior to the SMR October 2021 Release 1 security update. The vulnerability is in the modem interface driver, which is a common component across Samsung's Android device lineup.
How do I fix CVE-2021-25489?
The fix is to apply the Samsung SMR October 2021 Release 1 security update or any later security patch. Update the device through Settings > Software Update. Enterprise environments should use MDM solutions to push the update to all managed Samsung devices promptly.
How severe is CVE-2021-25489?
CVE-2021-25489 has a CVSS v3.1 score of 3.3, rated as Low severity, with impact limited to a denial-of-service condition through kernel panic. However, its inclusion in CISA's KEV catalog indicates real-world exploitation, likely as part of more complex attack chains. The EPSS score of 0.36% (58th percentile) suggests targeted rather than widespread exploitation.
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