CVE-2025-12829 is a medium-severity vulnerability classified as CWE-125 (Out-of-bounds Read) found in Amazon Ion-C, a C language library for Amazon Ion data serialization. The flaw exists in versions prior to v1.1.4 and involves an uninitialized stack read during the serialization process to Ion text format. Specifically, a threat actor can craft malicious input data that, when serialized, causes the library to read beyond the bounds of allocated memory on the stack. This out-of-bounds read can leak sensitive data residing in memory, which is then exposed through UTF-8 escape sequences in the serialized Ion text output. The vulnerability does not require any privileges or user interaction, but the attack vector is local (AV:L), meaning the attacker must have local access to the system running the vulnerable library. The vulnerability impacts confidentiality (VC:H) but not integrity or availability. The CVSS 4.0 vector indicates low attack complexity and no authentication required, but the limited attack vector reduces the overall exploitability. No public exploits or active exploitation have been reported to date. The recommended mitigation is to upgrade to Amazon Ion-C version 1.1.4 or later, where the issue has been fixed by properly initializing stack variables and preventing out-of-bounds reads during serialization.

For European organizations, the primary impact of CVE-2025-12829 is the potential exposure of sensitive in-memory data through crafted Ion text serialization. This could lead to leakage of confidential information, including cryptographic keys, personal data, or proprietary business information, depending on what resides in memory at the time of exploitation. Organizations using Amazon Ion-C in their software stacks—especially those processing sensitive data or operating in regulated sectors such as finance, healthcare, or government—face increased risk of data breaches. Although the attack requires local access, insider threats or compromised internal systems could exploit this vulnerability. The impact on system integrity and availability is negligible, but confidentiality breaches can have significant legal and reputational consequences under European data protection laws like GDPR. Additionally, organizations relying on cloud services or software components that embed Amazon Ion-C may be indirectly affected if those services are not promptly updated.

To mitigate CVE-2025-12829, European organizations should: 1) Immediately upgrade all instances of Amazon Ion-C to version 1.1.4 or later, where the vulnerability is patched. 2) Conduct an inventory of software and services that incorporate Amazon Ion-C to ensure no vulnerable versions remain in production or development environments. 3) Implement strict access controls and monitoring on systems running Ion-C to limit local access and detect suspicious activity that could indicate exploitation attempts. 4) Employ memory safety and integrity checks during software development and testing to catch similar issues early. 5) Coordinate with cloud service providers and third-party vendors to confirm that their platforms have applied the necessary updates. 6) Review and enhance insider threat detection programs, as local access is required for exploitation. 7) Maintain up-to-date incident response plans to quickly address any potential data exposure incidents stemming from this vulnerability.