CriticalPublic exploitVulnerability

CVE-2026-115893

Wasmtime Cranelift ARM64 br_table Sandbox Escape

Published Oct 23, 2026 · Updated today

Trending this week#91of 416,552 vulnerabilities

Mention activity · 30 days

20 mentions · peak 6 in a dayToday

CVSS9.9Critical · v3.1

EPSS0.43%37th percentile

CISA KEVNoNot listed

In the wildNonePublic exploit, no exploitation reported

IdentifiersCVE-2026-115893CWE-691 · Insufficient Control Flow Management

CVE-2026-115893 is a sandbox-escape vulnerability in Wasmtime's default Cranelift compiler backend on ARM64 (aarch64). When compiling a WebAssembly br_table instruction with more than approximately 256,000 targets, Cranelift can place the default target beyond the approximately 1 MiB reach of its conditional branch. The branch offset silently wraps, generating an incorrect destination and allowing an attacker-controlled module to redirect execution to arbitrary code at a user-controlled offset. Affected releases include versions before 36.0.19, versions 37.0.0 through 47.x, versions 48.0.0 through 48.0.6, and versions 49.0.0 through 49.0.3.

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Analyst brief

Impact, mitigation & remediation

What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can break WebAssembly sandbox isolation and execute code outside the module's intended environment. This can compromise the confidentiality, integrity, and availability of the embedding host process and potentially expose other tenants' data, depending on application privileges and workload isolation. A complete post-escape attack chain has not been established in the available information.

Mitigation

If you can’t patch tonight, do this now.

No vendor-supported workaround is specified. Pending an upgrade, restrict or suspend compilation of untrusted WebAssembly modules, authenticate and review module submissions, and reject unusually large modules or br_table instructions. Apply least privilege and strong operating-system isolation to limit the consequences of a sandbox escape. These measures reduce exposure but do not correct the compiler defect.

Remediation

Patch, then assume compromise.

Upgrade to Wasmtime 36.0.19, 48.0.7, 49.0.4, 50.0.0, or a later patched release appropriate to the deployment. Migrate unsupported release lines to a supported fixed version. Update embedded dependencies, rebuild and redeploy every affected application, and regenerate cached or precompiled modules using the patched compiler; updating only the standalone command-line tool does not fix embedded copies. The compiler fix routes the default case through the jump table rather than the limited-range conditional branch.

Public exploits

Exploits

1 exploit validated by Mallory's analysis.

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CVE-2026-115893-wasmtime-sandbox-escapeThis standalone exploit package targets the reported CVE-2026-115893 aarch64 Cranelift br_table miscompilation. Two Python generators emit import-free WebAssembly modules containing attacker-chosen AArch64 instructions in v128 constants. Cranelift places those constants in an executable JIT literal pool. An oversized jump table causes the default conditional branch displacement to wrap into that pool, executing the embedded payload. The macOS generator uses 524,255 targets and a reported destination of offset 0x50; the Linux generator uses 524,252 targets and offset 0x40. The exported pwn function supplies the index that selects the default branch. This provides native host code execution rather than merely a compiler crash. The 26 supplied files comprise two Python generators, two assembly payload sources, two shell verification scripts, documentation, checksums, disassembly, and execution/control logs. The lab directory supplies payload sources and inspection artifacts; evidence records vulnerable and fixed runs. The generated WAT files and screenshots referenced by documentation and CHECKSUMS.txt are absent from the supplied inventory. The verification scripts assume the WAT files already exist and do not generate them automatically. Repository-provided logs report successful marker creation in five macOS and three Linux runs on Wasmtime 49.0.3, with rejection in six corresponding 49.0.4 runs. A 65,520-target control creates no marker, supporting the oversized-table trigger. The documented fixes are 36.0.19, 48.0.7, and 49.0.4. These claims and CVE mappings were assessed from supplied material, not independently executed or externally verified. README and technical-writeup excerpts are truncated, and some historical evidence hashes differ from CHECKSUMS.txt. The exploit is build/layout-sensitive and is not version-blind. The implemented payload only executes /usr/bin/touch /tmp/wt-pwn. There are no network calls, listeners, exfiltration endpoints, or command-and-control infrastructure; GitHub URLs are documentation and acquisition references. Linux container demonstrations escape the Wasmtime sandbox only, not the container. CVE-2026-115889 is explicitly described as a separate issue and is not targeted. Repository URL was inferred from README; the analyzed git reference and archive size were not provided, represented as an empty string and 0.shreyas-malhotra · Disclosed Oct 27, 2026 · python · assembly · file · localOperational

External references

References

Activity feed

Recent activity

20 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

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csirt skNews · Oct 27, 2026Kritické zraniteľnosti Wasmtime vedú k úniku zo sandboxu | CSIRT.SKCritical Cranelift compiler vulnerability, rated CVSS 9.9, affecting Wasmtime on ARM64 (aarch64). Compiling a WebAssembly br_table instruction with more than 256,000 targets creates an oversized jump table. Out-of-range indices silently redirect execution to an incorrect default code location, where an attacker supplying the module can control the code, potentially enabling a sandbox escape. Exploitation requires a low-privileged remote attacker able to submit a crafted module. The advisory lists affected Wasmtime versions as earlier than 36.0.19, 37.0.0–42.x, 43.0.0–47.x, 48.0.0–48.0.6, and 49.0.0–49.0.3. Recommended fixed releases are 36.0.19, 48.0.7, 49.0.4, or 50.0.0; applications embedding vulnerable Wasmtime libraries should be rebuilt with an updated version.Read more ↗malware newsNews · Oct 27, 2026Wasmtime Sandbox Escape Flaws Patched in Cranelift - Malware News - Malware Analysis, News and IndicatorsCritical ARM64-specific Wasmtime sandbox escape rated CVSS 9.9. Cranelift incorrectly handles the default branch of very large WebAssembly br_table instructions, potentially breaking sandbox isolation under default settings. The article states that all ARM64-supporting versions since 2020 are affected until patched. Fixed releases are 36.0.19, 48.0.7, 49.0.4, and 50.0.0. The article reports no public PoC or known exploitation as of October 26, 2026. Upgrade, rebuild embedding applications, and recompile cached modules. Restricting untrusted compilation, screening unusually large modules, and strengthening host isolation can reduce exposure, but the advisory provides no workaround.Read more ↗socradar blogNews · Oct 27, 2026Wasmtime Sandbox Escape Flaws Patched in CraneliftA critical ARM64-specific Cranelift control-flow flaw rated CVSS 9.9 that can break Wasmtime sandbox isolation under default settings. The article states that affected versions extend back to the introduction of ARM64 support in 2020. Fixed releases include 36.0.19, 48.0.7, 49.0.4, and 50.0.0. Embedding applications must be rebuilt and cached modules recompiled. No advisory workaround is available; restricting untrusted modules and applying stronger host isolation can reduce exposure pending upgrades.Read more ↗the hacker newsNews · Oct 26, 2026Two Critical Wasmtime Flaws Could Let Malicious WebAssembly Modules Escape SandboxesA critical ARM64-only sandbox-escape vulnerability in Wasmtime's Cranelift compiler, rated CVSS 9.9. A WebAssembly br_table containing more than approximately 256,000 targets can exceed the roughly 1 MiB reach of the branch used for out-of-range indexes, silently redirecting execution to the wrong location. Exploitation requires compilation of an attacker-controlled module. The bug has existed since ARM64 support began in 2020. Fixed releases are 36.0.19, 48.0.7, 49.0.4, and 50.0.0 or later. The fix routes out-of-range indexes through the jump table and rejects tables exceeding 65,520 targets. Earlier April ARM64 sandbox-escape patches do not fix this vulnerability. Embedded applications require rebuilding with a fixed Wasmtime version. Neither advisory lists a workaround. The maintainers have not reported attacks, and the vulnerability was absent from CISA's KEV catalog as of October 26.Read more ↗

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Exposure mappingQuery your assets running an affected version, and investigate the blast radius.

Threat actor evidenceEvery report linking this CVE to a named adversary.

Associated malwareMalware families linked to this CVE, with evidence and IOCs.

Detection signaturesYARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mappingCross-references every affected SKU, including bundled OEM variants.

Social activity13Community discussion across Reddit, Mastodon, and other social sources.