GNU C Library iconv() Function Assertion Failure (CVE-2026-4046)

The GNU C Library (glibc) is a fundamental component of many Linux systems, providing core functionalities for applications. A vulnerability, CVE-2026-4046, exists within the iconv() function in glibc versions 2.43 and earlier. This flaw can be triggered when the library attempts to convert character sets from IBM1390 or IBM1399. If an application utilizes iconv() to process potentially malicious input from these character sets, it could lead to an assertion failure and subsequent crash. This vulnerability has a CVSS v3.1 score of 7.5 and may allow a remote attacker to cause a denial of service. While the vulnerability itself is within glibc, the impact is on applications which call the vulnerable function. Mitigation involves removing the vulnerable character sets from systems that do not need them.

Attack Chain

1. An attacker crafts malicious input data using the IBM1390 or IBM1399 character sets.
2. The attacker delivers the malicious input to a vulnerable application (e.g., via a network socket, file upload, or other means).
3. The vulnerable application receives the attacker-controlled input.
4. The application calls the iconv() function from the GNU C Library to convert the malicious input.
5. iconv() attempts to convert the IBM1390 or IBM1399 input.
6. An assertion failure occurs within the iconv() function due to the crafted input.
7. The application process terminates abruptly due to the assertion failure.
8. The application becomes unavailable, resulting in a denial-of-service condition.

Impact

Successful exploitation of CVE-2026-4046 can cause applications using the vulnerable iconv() function to crash. This can lead to a denial-of-service condition, impacting application availability and potentially disrupting business operations. The severity of the impact depends on the criticality of the affected application and the scope of its usage. Although the exact number of affected applications is unknown, any application relying on glibc's iconv() function for character set conversion, especially when handling external input, is potentially at risk.

Recommendation

• Apply the recommended mitigation of removing the IBM1390 and IBM1399 character sets from systems that do not require them. This can be done by modifying the glibc configuration files (reference: CVE-2026-4046 description).
• Monitor application logs for crashes related to iconv() function calls when handling IBM1390 or IBM1399 character sets.
• Deploy the Sigma rule Detect Iconv Crash to identify potential exploitation attempts based on application crash logs.