enter_l2_vcpu passes the wrong RCX operand to TDG.VP.ENTER

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

4.6 · CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-20763: 0.15% estimated exploitation activity in the next 30 days; percentile 4.15 (FIRST EPSS, 2026-11-10). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

`tdx_guest::tdcall::enter_l2_vcpu()` invokes the `TDG.VP.ENTER` TDCALL. RCX must carry the L2 VM index in bits 53:52 and the invalidation control value (`InvdTranslations`, 0 to 3) in bits 1:0. The function computed that value as `(l2_vm_idx << 52) | (invd_translations as u64)`, but then passed the raw `l2_vm_idx` in RCX instead. As a result, the TDX module received an operand that differs from the caller's request. The VM index field was 0, and the low bits of the index were interpreted as the invalidation control value. For example, VM 1 with `InvdTlb` (2) should produce `0x0010_0000_0000_0002`, but produced `0x1`. Intel describes the issue as an incorrect calculation and classifies it as escalation of privilege, with a CVSS 4.0 base score of 4.6, in INTEL-SA-01462. The flaw was corrected in commit `311d33b`, released in 0.3.1, which passes the computed RCX value.…

Published by the source

11 Aug 2026, 12:00 UTC

Last modified by the source

11 Nov 2026, 08:45 UTC

Source last checked

12 Nov 2026, 06:15 UTC

1. Revision 1 · created · 12 Nov 2026

   Published from osv record RUSTSEC-2026-0485

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# Patch Next advisory brief: CVE-2026-20763

Advisory: `enter_l2_vcpu` passes the wrong RCX operand to `TDG.VP.ENTER`
IDs: CVE-2026-20763, GHSA-wgvc-hf5h-m5h7
Record: https://patchnext.com/advisories/cve-2026-20763 (revision 1, source checked 12 Nov 2026, 06:15 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tdx-guest 0.3.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io tdx-guest: affected >= 0.1.8, < 0.3.1; fixed in 0.3.1

## Suggested inspection (read-only)
- crates.io tdx-guest: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on tdx-guest.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/RUSTSEC-2026-0485 (OSV record RUSTSEC-2026-0485 lists affected ranges: crates.io tdx-guest >=0.1.8 <0.3.1 (fixed))

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