CVE-2026-34988 Vulnerability Analysis & Exploit Details

CVE-2026-34988 Vulnerability Summary

CVE-2026-34988: Wasmtime is a runtime for WebAssembly. From 28.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of its pooling allocator contains a bug where in certain configurations the contents of linear memory can be leaked from one instance to the next. The implementation of resetting the virtual memory permissions for linear memory used the wrong predicate to determine if resetting was necessary, where the compilation process used a different predicate. This divergence meant that the pooling allocator incorrectly deduced at runtime that resetting virtual memory permissions was not necessary while compile-time determine that virtual memory could be relied upon. The pooling allocator must be in use, Config::memory_guard_size configuration option must be 0, Config::memory_reservation configuration must be less than 4GiB, and pooling allocator must be configured with max_memory_size the same as the memory_reservation value in order to exploit this vulnerability. If all of these conditions are applicable then when a linear memory is reused the VM permissions of the previous iteration are not reset. This means that the compiled code, which is assuming out-of-bounds loads will segfault, will not actually segfault and can read the previous contents of linear memory if it was previously mapped. This represents a data leakage vulnerability between guest WebAssembly instances which breaks WebAssembly's semantics and additionally breaks the sandbox that Wasmtime provides. Wasmtime is not vulnerable to this issue with its default settings, nor with the default settings of the pooling allocator, but embeddings are still allowed to configure these values to cause this vulnerability. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.

CVE-2026-34988 References

External References

• https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-6wgr-89rj-399p

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• Buffer Overflow via Environment Variables CAPEC-10 This attack pattern involves causing a buffer overflow through manipulation of environment variables. Once the adversary finds that they can modify an environment variable, they may try to overflow associated buffers. This attack leverages implicit trust often placed in environment variables.
• Overflow Buffers CAPEC-100 Buffer Overflow attacks target improper or missing bounds checking on buffer operations, typically triggered by input injected by an adversary. As a consequence, an adversary is able to write past the boundaries of allocated buffer regions in memory, causing a program crash or potentially redirection of execution as per the adversaries' choice.
• Buffer Manipulation CAPEC-123 An adversary manipulates an application's interaction with a buffer in an attempt to read or modify data they shouldn't have access to. Buffer attacks are distinguished in that it is the buffer space itself that is the target of the attack rather than any code responsible for interpreting the content of the buffer. In virtually all buffer attacks the content that is placed in the buffer is immaterial. Instead, most buffer attacks involve retrieving or providing more input than can be stored in the allocated buffer, resulting in the reading or overwriting of other unintended program memory.
• Client-side Injection-induced Buffer Overflow CAPEC-14 This type of attack exploits a buffer overflow vulnerability in targeted client software through injection of malicious content from a custom-built hostile service. This hostile service is created to deliver the correct content to the client software. For example, if the client-side application is a browser, the service will host a webpage that the browser loads.
• Filter Failure through Buffer Overflow CAPEC-24 In this attack, the idea is to cause an active filter to fail by causing an oversized transaction. An attacker may try to feed overly long input strings to the program in an attempt to overwhelm the filter (by causing a buffer overflow) and hoping that the filter does not fail securely (i.e. the user input is let into the system unfiltered).
• MIME Conversion CAPEC-42 An attacker exploits a weakness in the MIME conversion routine to cause a buffer overflow and gain control over the mail server machine. The MIME system is designed to allow various different information formats to be interpreted and sent via e-mail. Attack points exist when data are converted to MIME compatible format and back.
• Overflow Binary Resource File CAPEC-44 An attack of this type exploits a buffer overflow vulnerability in the handling of binary resources. Binary resources may include music files like MP3, image files like JPEG files, and any other binary file. These attacks may pass unnoticed to the client machine through normal usage of files, such as a browser loading a seemingly innocent JPEG file. This can allow the adversary access to the execution stack and execute arbitrary code in the target process.
• Buffer Overflow via Symbolic Links CAPEC-45 This type of attack leverages the use of symbolic links to cause buffer overflows. An adversary can try to create or manipulate a symbolic link file such that its contents result in out of bounds data. When the target software processes the symbolic link file, it could potentially overflow internal buffers with insufficient bounds checking.
• Overflow Variables and Tags CAPEC-46 This type of attack leverages the use of tags or variables from a formatted configuration data to cause buffer overflow. The adversary crafts a malicious HTML page or configuration file that includes oversized strings, thus causing an overflow.
• Buffer Overflow via Parameter Expansion CAPEC-47 In this attack, the target software is given input that the adversary knows will be modified and expanded in size during processing. This attack relies on the target software failing to anticipate that the expanded data may exceed some internal limit, thereby creating a buffer overflow.
• Buffer Overflow in an API Call CAPEC-8 This attack targets libraries or shared code modules which are vulnerable to buffer overflow attacks. An adversary who has knowledge of known vulnerable libraries or shared code can easily target software that makes use of these libraries. All clients that make use of the code library thus become vulnerable by association. This has a very broad effect on security across a system, usually affecting more than one software process.
• Buffer Overflow in Local Command-Line Utilities CAPEC-9 This attack targets command-line utilities available in a number of shells. An adversary can leverage a vulnerability found in a command-line utility to escalate privilege to root.

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