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NVD / CVE Program· CNA GitHub_M

CVE-2026-34943: Wasmtime panics when lifting `flags` component value

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.33% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. Administrator privileges are required. Special conditions such as timing or configuration are required.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: bytecodealliance wasmtime 24.0.7.

Low priority for now. Upgrade to bytecodealliance wasmtime 24.0.7 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a possible panic which can happen when a flags-typed component model value is lifted with the Val type. If bits are set outside of the set of flags the component model specifies that these bits should be ignored but Wasmtime will panic when this value is lifted. This panic only affects wasmtime's implementation of lifting into Val, not when using the flags! macro. This additionally only affects flags-typed values which are part of a WIT interface. This has the risk of being a guest-controlled panic within the host which Wasmtime considers a DoS vector. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.

MediumCVSS 5.6 · v4.0—No exploit Fix available
Published
Apr 9, 2026
Updated
Oct 26, 2026
EPSS
0.3% · 27th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.6 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
5.6
NVD has not scored this yet; the score shown is the CNA’s.

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-34943

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
bytecodealliancewasmtime

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • bytecodealliance wasmtimebefore 24.0.7
  • bytecodealliance wasmtime25.0.0 and later · before 36.0.7
  • bytecodealliance wasmtime37.0.0 and later · before 42.0.2
  • bytecodealliance wasmtime43.0.0 and later · before 43.0.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • bytecodealliance wasmtime

    • < 24.0.7, >= 25.0.0, < 36.0.7, >= 37.0.0, < 42.0.2, >= 43.0.0, < 44.0.1affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
crates.iowasmtimefrom 0.0.0-0 · before 24.0.724.0.7
crates.iowasmtimefrom 25.0.0 · before 36.0.736.0.7
crates.iowasmtimefrom 37.0.0 · before 42.0.242.0.2
crates.iowasmtimefrom 43.0.0 · before 43.0.143.0.1
crates.iowasmtimebefore 24.0.724.0.7
Debian:13rust-wasmtimefrom 0—
Debian:14rust-wasmtimebefore 36.0.7+dfsg-136.0.7+dfsg-1
openSUSE:Tumbleweedtree-sitterbefore 0.26.8-2.10.26.8-2.1

Same product

bytecodealliance: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-115893Wasmtime: Cranelift backend on aarch64 can jump to incorrect target on large Wasm `br_table` instruction
    39Monitor
  • CVE-2026-115889Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
    39Monitor
  • CVE-2022-39394wasmtime_trap_code C API function has out of bounds write vulnerability
    39Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-34941Apr 9, 2026 · Wasmtime has a Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding
    27Monitor
  • ← EarlierCVE-2026-34942Apr 9, 2026 · Wasmtime panics when transcoding misaligned utf-16 strings
    23Monitor
  • Later →CVE-2026-34944Apr 9, 2026 · Wasmtime segfault or unused out-of-sandbox load with `f64x2.splat` operator on x86-64
    16Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
bytecodealliance wasmtime24.0.7 · descriptionVendor (CNA)
crates.io:wasmtime24.0.7Package registry (OSV)
crates.io:wasmtime36.0.7Package registry (OSV)
crates.io:wasmtime42.0.2Package registry (OSV)
crates.io:wasmtime43.0.1Package registry (OSV)
debian:rust-wasmtime36.0.7+dfsg-1 · Debian:14Package registry (OSV)
opensuse:tree-sitter0.26.8-2.1 · openSUSE:TumbleweedPackage registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-115892197 days apartWasmtime: Panic lowering a host-created component model stream into a guest that expects a different payload type
    22Monitor
  • CVE-2026-349440 days apartWasmtime segfault or unused out-of-sandbox load with `f64x2.splat` operator on x86-64
    16Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • Administrator privileges are required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
High
Privileges required
High
User interaction
A
Scope
X

Weakness class (CWE)

CWE-248 · Uncaught Exception

CVSS vector

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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records