GHSA-243v-98vx-264h CVE-2026-27572 RUSTSEC-2026-0021

Wasmtime can panic when adding excessive fields to a `wasi:http/types.fields` instance

High crates.io

Severity: 0.0 / 10; High · CVSS 4.0
Exploit chance (EPSS): 0.52%; Chance of exploitation in the next 30 days. Higher than 44.10% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-770 Allocation of Resources Without Limits or Throttling
Fix: 24.0.6; Upgrade wasmtime to this version or later

Description

Impact

Wasmtime's implementation of the wasi:http/types.fields resource is susceptible to panics when too many fields are added to the set of headers. Wasmtime's implementation in the wasmtime-wasi-http crate is backed by a data structure which panics when it reaches excessive capacity and this condition was not handled gracefully in Wasmtime. Panicking in a WASI implementation is a Denial of Service vector for embedders and is treated as a security vulnerability in Wasmtime.

Patches

Wasmtime 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0 patch this vulnerability and return a trap to the guest instead of panicking.

Workarounds

There are no known workarounds at this time, embedders are encouraged to update to a patched version of Wasmtime.

Resources

Limitations of http::HeaderMap

Affected versions

crates.io

Package	Vulnerable	Fixed in
wasmtime	`< 24.0.6`	`24.0.6`
wasmtime	`>= 25.0.0, < 36.0.6`	`36.0.6`
wasmtime	`>= 37.0.0, < 40.0.4`	`40.0.4`
wasmtime	`>= 0.0.0-0, < 24.0.6` `>= 25.0.0, < 36.0.6` `>= 37.0.0, < 40.0.4` `>= 41.0.0, < 41.0.4`	`24.0.6` `36.0.6` `40.0.4` `41.0.4`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

wasmtime crates.io → `24.0.6`

cargo

cargo update -p wasmtime --precise 24.0.6

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

Attack vector: Network
Attack complexity: Low
Attack requirements: Present
Privileges required: Low
User interaction: Passive
Confidentiality (vulnerable system): None
Integrity (vulnerable system): None
Availability (vulnerable system): High
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): High

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Weakness

CWE-770: Allocation of Resources Without Limits or Throttling

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

How to prevent it

Requirements: Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design: Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place, and it will help the administrator to identify who is committing the abuse. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, typically by using increasing time delays uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution can be difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply requires more resources on the part of the attacker.
Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
Architecture and Design, Implementation: If the program must fail, ensure that it fails gracefully (fails closed). There may be a temptation to simply let the program fail poorly in cases such as low memory conditions, but an attacker may be able to assert control before the software has fully exited. Alternately, an uncontrolled failure could cause cascading problems with other downstream components; for example, the program could send a signal to a downstream process so the process immediately knows that a problem has occurred and has a better chance of recovery. Ensure that all failures in resource allocation place the system into a safe posture.
Operation, Architecture and Design: Use quotas or other resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2026-27572

Packages

Timeline

Feb 24, 2026 Published
Oct 12, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
RUSTSEC-2026-0424 Unchecked memory usage in transferring borrowed resources between components	Not rated yet	Also affects wasmtime
RUSTSEC-2026-0423 Cross-engine type confusion with host-created struct-types-with-supertypes	Not rated yet	Also affects wasmtime
RUSTSEC-2026-0422 Typed functions with `i31` or `nullref` arguments may panic due to insufficient type-check	Low	Also affects wasmtime
RUSTSEC-2026-0379 Wasmtime: Cranelift backend on aarch64 can jump to incorrect target on large Wasm `br_table` instruction	Critical	Also affects wasmtime
GHSA-9pvw-hwfg-92h5 Wasmtime: Panic lowering a host-created component model stream into a guest that expects a different payload type	Medium	Also affects wasmtime
GHSA-897f-g5gm-fmxm Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation	Critical	Also affects wasmtime
RUSTSEC-2026-0364 Exception tags can cause host data structures to be unaligned	Not rated yet	Also affects wasmtime
RUSTSEC-2026-0363 Component-model handle tables are capped only per instance and charged to no limit	Medium	Also affects wasmtime

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