CVE-2026-120243 in FFmpeg
Summary
by MITRE • 11/01/2026
FFmpeg 2.0 through 9.0.2 contains a use of uninitialized variable vulnerability in the Go2Meeting decoder that allows attackers to leak stack memory through out-of-range palette indices. Attackers can craft a G2M3/G2M4 stream with a short Kempf palette so kempf_restore_buf() copies uninitialized stack bytes, including pointers or stack guards, into decoded output.
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Analysis
by VulDB Data Team • 11/01/2026
The vulnerability identified in FFmpeg versions 2.0 through 9.0.2 represents a critical memory safety flaw within the Go2Meeting video decoder component. This issue stems from improper initialization of variables used during the decoding process, specifically when handling palette data for G2M3 and G2M4 stream formats. The core technical failure occurs in the kempf_restore_buf function, which is responsible for restoring buffer states based on palette indices provided by the input media file. When an attacker crafts a malicious video stream with a deliberately short Kempf palette, the decoder fails to validate that subsequent index references fall within the bounds of this reduced palette structure. Consequently, the decoding logic proceeds to access memory locations beyond the allocated and initialized boundaries of the palette array.
This out-of-bounds read operation results in the copying of uninitialized stack bytes into the decoded output buffer. Because these uninitialized regions often contain sensitive data from previous function calls or local variable allocations on the call stack, the vulnerability effectively allows for arbitrary information leakage. The leaked data can include critical system artifacts such as memory pointers, which may facilitate further exploitation by revealing address space layout randomization (ASLR) bypasses, or stack guard values that could be used to defeat stack protection mechanisms like canaries. This type of flaw is classified under CWE-457, which denotes the use of an uninitialized variable, and aligns with ATT&CK technique T1005, indicating data from local system memory extraction capabilities for reconnaissance purposes.
The operational impact of this vulnerability extends beyond simple information disclosure. While primarily categorized as a confidentiality breach due to stack memory leakage, such vulnerabilities often serve as precursors to more severe exploits in complex media processing pipelines. By leaking pointers or internal state information, an attacker gains valuable intelligence about the target environment's memory layout and security configurations. This knowledge can significantly lower the barrier for subsequent attacks, including remote code execution if combined with other exploitation techniques that leverage leaked addresses to overwrite function pointers or return addresses. The presence of stack guards in the leaked data also indicates potential weaknesses in how FFmpeg manages its internal state during video decoding operations.
Mitigation strategies must prioritize immediate software updates and defensive coding practices. Users running affected versions of FFmpeg should upgrade to version 9.0.3 or later, where this specific initialization flaw has been addressed by developers through stricter bounds checking and proper variable initialization routines within the Go2Meeting decoder module. For organizations unable to patch immediately, deploying input validation layers at network boundaries can help filter out malformed G2M streams before they reach the FFmpeg processing engine. Additionally, enabling compiler-based security features such as stack protectors and Address Sanitizer during development builds is recommended to detect similar uninitialized memory access patterns early in the software lifecycle. Regular auditing of media parsing libraries against CWE standards ensures that future implementations adhere to secure coding guidelines regarding array bounds and variable initialization states.