Samsung rlottie: RCE Bug in Lottie Files Masked by a "Medium"…

A numeric truncation flaw in Samsung rlottie enables remote code execution via malicious Lottie animations. The CVSS 5.5 rating understates the risk for applications that load untrusted files.

On July 15, 2026, Trend Micro's Zero Day Initiative published advisory ZDI-26-422 detailing a vulnerability in Samsung rlottie, an open-source library for rendering Lottie animations. The flaw allows arbitrary remote code execution via maliciously crafted animation files. The CVE-2026-15551 record assigns the vulnerability a score of 5.5, classified as MEDIUM.

Key Takeaways

The vulnerability CVE-2026-15551 resides in Samsung rlottie's gray_hline() function and enables remote code execution via malicious animated Lottie files.
The mechanism is a numeric truncation that causes an integer overflow, leading to a heap-based buffer overflow during memory size calculation.
Samsung released a patch in commit bf689b72b8482c5ea674235854bd11b6d1b42588, made public after 19 days of coordinated disclosure with ZDI.
The CVSS 5.5 originates from the CVE record, not the ZDI advisory, which does not report it. The vector AV:L/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:H reflects attack constraints that depend on implementation.

The Numeric Truncation Mechanism in `gray_hline()`

The flaw lies in the gray_hline() function, a rendering routine in the rlottie library. According to the CVE-2026-15551 record, a numeric truncation in this function leads to an incorrect memory size calculation prior to writing: the integer overflow or wraparound triggers a heap-based buffer overflow when the library processes a Lottie animation crafted to render at the canvas's native dimensions.

The ZDI advisory states that "the issue results from the lack of proper validation of user-supplied data, which can result in an incorrect calculation before writing to memory." An attacker who controls the content of a Lottie file can trigger this sequence to execute code in the context of the process performing the rendering. Exploitation requires interaction with the rlottie library; attack vectors "may vary depending on the implementation."

The Lottie format serializes animations into JSON readable by software and hardware rendering engines. Samsung rlottie is one of the most widely deployed native implementations, particularly in mobile and embedded contexts. The library is designed to be embedded as a dependency in third-party applications.

The CVSS 5.5 and Its Documented Limits

The CVSS 5.5 score with vector AV:L/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:H comes from the CVE-2026-15551 record, not the ZDI advisory, which does not include it. These parameters reflect formal technical constraints: local attack, high complexity, low privileges required, user interaction required, unchanged scope.

Analysis: CVSS measures vulnerability severity in its abstract attack context. When an application loads Lottie files from untrusted sources, the "local" in the AV:L vector refers to the process context; it does not imply the attacker must first compromise the system. User interaction (UI:R) is required for exploitation per the CVSS model, but the source does not specify in which implementations this interaction is visible or transparent.

DeafNews Perspective: The discrepancy between RCE capability and a MEDIUM rating is not a flaw in CVSS itself, but a consequence of its architecture: the system does not model the payload delivery path or the popularity of the target format.

"This vulnerability allows remote attackers to execute arbitrary code on affected installations of Samsung rlottie. Interaction with the rlottie library is required to exploit this vulnerability but attack vectors may vary depending on the implementation." — Advisory ZDI-26-422

Coordinated Disclosure and the Patch Commit

Researcher Michael DePlante, known as @izobashi, reported the vulnerability to Samsung on June 26, 2026. ZDI managed the coordinated disclosure with public release on July 15, 2026: a 19-day window.

The CVE-2026-15551 record identifies the non-vulnerable version as commit bf689b72b8482c5ea674235854bd11b6d1b42588. The source does not specify whether this commit has been backported to previous maintenance branches. The dossier does not document patch distribution through automatic channels such as package managers, nor does it confirm that Samsung has published a separate advisory of its own.

Immediate Actions

Teams managing applications with a dependency on Samsung rlottie must verify the library's presence in their dependency tree and compare the current commit against bf689b72b8482c5ea674235854bd11b6d1b42588. The source does not specify automatic patch distribution channels.

Source Limitations: The ZDI advisory is published on an HTTP (non-HTTPS) domain and does not report the CVSS score. The 5.5 score comes from the separate CVE record. No public exploit is documented. Patch distribution remains unclear.

The Limits of Scoring and the Lesson for Threat Modeling

CVE-2026-15551 illustrates a case where formal classification may not align with the risk for specific implementations. For organizations loading Lottie files from untrusted sources, the MEDIUM classification may not reflect the actual risk.

Analysis: The 5.5 score for CVE-2026-15551 is mathematically consistent with the declared vector, but its practical applicability depends on the architecture of each system integrating rlottie. The decision to prioritize patching remains a risk management assessment based on specific operational context.

The case raises questions about how development teams interpret CVSS scores for complex format-parsing components, without the brief providing generalizable operational recommendations beyond the documented context.

Information verified against cited sources and current as of publication.

Sources

Sources and references

The Numeric Truncation Mechanism in gray_hline()