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Wasmtime vulnerable to segfault when using component resources

Low severity GitHub Reviewed Published Oct 24, 2025 in bytecodealliance/wasmtime • Updated Oct 27, 2025

Package

cargo wasmtime (Rust)

Affected versions

>= 38.0.0, < 38.0.3

Patched versions

38.0.3

Description

Impact

The implementation of component-model related host-to-wasm trampolines in Wasmtime contained a bug where it's possible to carefully craft a component, which when called in a specific way, would crash the host with a segfault or assert failure. This bug was introduced in the release of Wasmtime 38.0.0 and affects it subsequent patch releases of 38.0.1 and 38.0.2. No other versions of Wasmtime are affected.

In Wasmtime 38 the implementation of host-to-wasm trampolines was refactored to remove the old usage of setjmp and longjmp to unwind the stack. In this transition, however, trampolines for component-model intrinsics were accidentally not updated meaning that they didn't update runtime data structures as the other host-to-wasm trampolines did. If an error ocurred during execution of wasm it would then try to read this runtime data which isn't present, and processing it could then result in a crash. For example one piece of runtime data is where to jump to in the case of a trap, and this is intended to be updated by trampolines during their execution. In this situation the trampoline didn't do anything meaning that the value was left set to 0 meaning that execution would jump to the 0 address and deterministically crash the program with a segfault.

Component intrinsic host-to-wasm trampolines are not typically used in most situations. These only exist for carefully crafted components no toolchain would conventionally produce. For example if the resource.rep intrinsic were directly lifted without having any other wasm in play then it would use the component intrinsic host-to-wasm trampoline. This effectively means that any component required to trigger this bug would have to be carefully crafted for this specific issue. Furthermore triggering this bug would require that these intrinsics are called from the host which requires specific type signatures to be used. Not all embeddings may be invoking functions with exactly the right type signatures, meaning that even if a component could be crafted a pre-built embedding may still not be able to run the component.

Overall the goal of Wasmtime's API is that, without unsafe in Rust, it should not be possible to crash the runtime. With Wasmtime 38.0.{0,1,2} it is possible to crash the runtime, however, hence this security issue. Actually exploiting this in practice would require (a) carefully crafted components, (b) a very specific host embedder using the right type signatures, and (c) a host that updated to 38.0.{0,1,2} within the last few days (38.0.0 was released on 2025-10-20, and this is being published on 2025-10-24). This likely means that almost no embedding is affected, but this security issue is nonetheless being posted for awareness.

Patches

Wasmtime 38.0.3 has been released and is patched to fix this issue.

Workarounds

Affected embeddings have no workaround other than updating to 38.0.3. Users of 37.0.x and prior are not affected. Embeddings that only work with core wasm are not affected. Embeddings may only be affected if functions of specific component type signatures are used/invoked, meaning that if all the prior conditions hold the embedding would need to be audited to see if it's affected.

References

The PR which refactored setjmp/longjmp usage and introduced this issue is bytecodealliance/wasmtime#11592.

References

@alexcrichton alexcrichton published to bytecodealliance/wasmtime Oct 24, 2025
Published by the National Vulnerability Database Oct 24, 2025
Published to the GitHub Advisory Database Oct 27, 2025
Reviewed Oct 27, 2025
Last updated Oct 27, 2025

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity High
Attack Requirements Present
Privileges Required Low
User interaction Passive
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability Low
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability Low

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(12th percentile)

Weaknesses

Improper Handling of Exceptional Conditions

The product does not handle or incorrectly handles an exceptional condition. Learn more on MITRE.

CVE ID

CVE-2025-62711

GHSA ID

GHSA-4h67-722j-5pmc

Source code

Credits

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