Evidence used
- No CISA KEV confirmation is currently recorded.
- A structured source references public exploit or proof-of-concept material.
- EPSS is 1.62% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2021
CVE-2021-43790High confidence
Use After Free in lucet
bytecodealliance · lucet
Official source article: GitHub GHSA-HF79-8HJP-RRVQ ↗. Check the applicable product and release in the original source.
8.5HighCVSS 3.1
Within 7 days
Patch availableHigh technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityHigh→Operational priority:Critical, raised one band.upgradedsince 4 Aug 2024
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Increase monitoring for the attack path and post-exploitation behaviour described in the report.
Verification
- Confirm that the asset runs bytecodealliance lucet and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Open-source package ranges1 source-attributed range
These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.
| Ecosystem and package | Affected range | First fixed version | Evidence |
|---|---|---|---|
| rustlucet-runtime | <= 0.6.1 | Not stated | GitHub advisory ↗upstream repository advisory · 20 Jan 2026 |
High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.
Patch available01
What, why and how
Lucet is a native WebAssembly compiler and runtime. There is a bug in the main branch of `lucet-runtime` affecting all versions published to crates.io that allows a use-after-free in an Instance object that could result in memory corruption, data race, or other related issues. This bug was introduced early in the development of Lucet and is present in all releases. As a result of this bug, and dependent on the memory backing for the Instance objects, it is possible to trigger a use-after-free when the Instance is dropped. Users should upgrade to the main branch of the Lucet repository. Lucet no longer provides versioned releases on crates.io. There is no way to remediate this vulnerability without upgrading.
What
Lucet is a native WebAssembly compiler and runtime. There is a bug in the main branch of `lucet-runtime` affecting all versions published to crates.io that allows a use-after-free in an Instance object that could result in memory corruption, data race, or other related issues. This bug was introduced early in the development of Lucet and is present in all releases. As a result of this bug, and dependent on the memory backing for the Instance objects, it is possible to trigger a use-after-free when the Instance is dropped. Users should upgrade to the main branch of the Lucet repository. Lucet no longer provides versioned releases on crates.io. There is no way to remediate this vulnerability without upgrading.
Why
The program can continue using memory after it has been released, producing unsafe and attacker-influenceable behaviour.
How
An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
Lucet is a native WebAssembly compiler and runtime. There is a bug in the main branch of `lucet-runtime` affecting all versions published to crates.io that allows a use-after-free in an Instance object that could result in memory corruption, data race, or other related issues. This bug was introduced early in the development of Lucet and is present in all releases. As a result of this bug, and dependent on the memory backing for the Instance objects, it is possible to trigger a use-after-free when the Instance is dropped. Users should upgrade to the main branch of the Lucet repository. Lucet no longer provides versioned releases on crates.io. There is no way to remediate this vulnerability without upgrading.
Why
The program can continue using memory after it has been released, producing unsafe and attacker-influenceable behaviour.
How
An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material Reference recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.
- Likely attack path
- a network path → Use After Free → cause the confidentiality, integrity or availability impact described by the vendor
- Attack surface
- Network
- Privileges required
- Low: a basic authenticated account is required
- User interaction
- None
- Attack complexity
- High: exploitation depends on specific conditions
- Security boundary
- Changed: exploitation can affect a different security authority
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-416 ↗
CWE-416: Use After Free. The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:HCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SChangedScope: The attack can affect a component governed by a different security authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.- Post-exploitation / living off the land
- No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
03
Patch and workaround
Operational remediation based on structured source evidence.
- Status
?
Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change. - Patch available
- Affected
- lucet: <= 0.6.1
- Action
- Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
- Workaround
- No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 29 Nov 2021 · Last source change 4 Aug 2024, 04:03 UTC · CWE-416 · Use After Free
CVE recordCVE.org · 5.1
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-14
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2021-2355
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD modified after enrichment
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.
CVE published
Fixed release or patch reference recorded
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.