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CVE-2026-34988
ANC
Low

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…

CVSS
2.3
Low
EPSS
0.00
p20
Published
2026-01-01
Updated
2026-01-01
Description

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.

Tags · CWE
RCE
CWE-119
CAPEC-8
CAPEC-9
CAPEC-10
CAPEC-14
CAPEC-24
CAPEC-42
CAPEC-44
CAPEC-45
CAPEC-46
CAPEC-47
CAPEC-100
CAPEC-123
Affected products
Wasmtime 28.0.0–36.0.7Wasmtime 37.0.0–42.0.2Wasmtime
CVSS vector
CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Timeline
2026-01-01
Published
2026-01-01
Updated
CVSS 3.1 breakdown
Attack Vector
AV: N
Network (N)
Attack Complexity
AC: H
High (H)
Attack Requirements
AT: P
Present
Privileges Required
PR: L
Low (L)
User Interaction
UI: N
None (N)
Vulnerable System Confidentiality
VC: L
Low (L)
Vulnerable System Integrity
VI: N
None (N)
Vulnerable System Availability
VA: N
None (N)
Subsequent System Confidentiality
SC: L
Low (L)
Subsequent System Integrity
SI: N
None (N)
Subsequent System Availability
SA: N
None (N)
Exploit Code Maturity
E: X
Not Defined
Confidentiality Requirement
CR: X
Not Defined
Integrity Requirement
IR: X
Not Defined
Availability Requirement
AR: X
Not Defined
Modified Attack Vector
MAV: X
Not Defined
Modified Attack Complexity
MAC: X
Not Defined
Modified Attack Requirements
MAT: X
Not Defined
Modified Privileges Required
MPR: X
Not Defined
Modified User Interaction
MUI: X
Not Defined
Modified Vulnerable System Confidentiality
MVC: X
Not Defined
Modified Vulnerable System Integrity
MVI: X
Not Defined
Modified Vulnerable System Availability
MVA: X
Not Defined
Modified Subsequent System Confidentiality
MSC: X
Not Defined
Modified Subsequent System Integrity
MSI: X
Not Defined
Modified Subsequent System Availability
MSA: X
Not Defined
s
S: X
X
au
AU: X
X
r
R: X
X
v
V: X
X
re
RE: X
X
u
U: X
X
Exploit indicators
EPSS
0.003 · p20
Known exploited (KEV)
No
Known exploits — Сканер-ВС
No Сканер-ВС checks registered for this vulnerability yet.
Affected products
ProductVendorStatus
Tracked
rust-wasmtimeTracked
rust-wasmtimeTracked
wasmtime*Tracked