vulnerability / NVI-00011870 / Revision 2
Wasmtime: WASI hard links bypass wasmtime-wasi's FilePerms for destination
GitHub lists this reviewed advisory for wasmtime-wasi, wasmtime-wasi, wasmtime-wasi, wasmtime-wasi. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.5 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
0.171%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.06463. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
wasmtime-wasi
source listed< 24.0.11
## Summary Wasmtime's WASI filesystem implementation lets a guest with a read-only source file capability overwrite that file by hard-linking it into another preopen that allows file writes. An attacker who can run a WASI guest can bypass `WasiCtxBuilder` per-preopen `FilePerms` and modify host files that were exposed as `FilePerms::READ`. This attack is possible through the wasip1, wasip2, and wasip3 interfaces to the WASI filesystem. This attack is also possible through an indirection of renaming a hardlink into another preopen. ### Details `WasiCtxBuilder::preopened_dir` documents `file_perms` as the maximum permissions usable for files in that preopen. However, hard-link creation and renaming only checked directory mutation for permission, and not whether the file permissions matched. This makes an attack possible where: * a read-only file `target` exists in a preopen with only FilePerms::READ * a hardlink named `alias`, with destination to the `target`, is created in a preopen with FilePerms::READ | FilePerms::WRITE * the attacker opens the file `alias` for writing, in which they can overwrite `target` The same attack is possible by way of renaming: * a read-only file `
wasmtime-wasi
source listed>= 25.0.0, < 36.0.12
## Summary Wasmtime's WASI filesystem implementation lets a guest with a read-only source file capability overwrite that file by hard-linking it into another preopen that allows file writes. An attacker who can run a WASI guest can bypass `WasiCtxBuilder` per-preopen `FilePerms` and modify host files that were exposed as `FilePerms::READ`. This attack is possible through the wasip1, wasip2, and wasip3 interfaces to the WASI filesystem. This attack is also possible through an indirection of renaming a hardlink into another preopen. ### Details `WasiCtxBuilder::preopened_dir` documents `file_perms` as the maximum permissions usable for files in that preopen. However, hard-link creation and renaming only checked directory mutation for permission, and not whether the file permissions matched. This makes an attack possible where: * a read-only file `target` exists in a preopen with only FilePerms::READ * a hardlink named `alias`, with destination to the `target`, is created in a preopen with FilePerms::READ | FilePerms::WRITE * the attacker opens the file `alias` for writing, in which they can overwrite `target` The same attack is possible by way of renaming: * a read-only file `
wasmtime-wasi
source listed>= 37.0.0, < 45.0.3
## Summary Wasmtime's WASI filesystem implementation lets a guest with a read-only source file capability overwrite that file by hard-linking it into another preopen that allows file writes. An attacker who can run a WASI guest can bypass `WasiCtxBuilder` per-preopen `FilePerms` and modify host files that were exposed as `FilePerms::READ`. This attack is possible through the wasip1, wasip2, and wasip3 interfaces to the WASI filesystem. This attack is also possible through an indirection of renaming a hardlink into another preopen. ### Details `WasiCtxBuilder::preopened_dir` documents `file_perms` as the maximum permissions usable for files in that preopen. However, hard-link creation and renaming only checked directory mutation for permission, and not whether the file permissions matched. This makes an attack possible where: * a read-only file `target` exists in a preopen with only FilePerms::READ * a hardlink named `alias`, with destination to the `target`, is created in a preopen with FilePerms::READ | FilePerms::WRITE * the attacker opens the file `alias` for writing, in which they can overwrite `target` The same attack is possible by way of renaming: * a read-only file `
wasmtime-wasi
source listed>= 46.0.0, < 46.0.1
## Summary Wasmtime's WASI filesystem implementation lets a guest with a read-only source file capability overwrite that file by hard-linking it into another preopen that allows file writes. An attacker who can run a WASI guest can bypass `WasiCtxBuilder` per-preopen `FilePerms` and modify host files that were exposed as `FilePerms::READ`. This attack is possible through the wasip1, wasip2, and wasip3 interfaces to the WASI filesystem. This attack is also possible through an indirection of renaming a hardlink into another preopen. ### Details `WasiCtxBuilder::preopened_dir` documents `file_perms` as the maximum permissions usable for files in that preopen. However, hard-link creation and renaming only checked directory mutation for permission, and not whether the file permissions matched. This makes an attack possible where: * a read-only file `target` exists in a preopen with only FilePerms::READ * a hardlink named `alias`, with destination to the `target`, is created in a preopen with FilePerms::READ | FilePerms::WRITE * the attacker opens the file `alias` for writing, in which they can overwrite `target` The same attack is possible by way of renaming: * a read-only file `
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-4ch3-9j33-3pmj ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-58494 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.