CVE-2021-29657: linux linux_kernel
Vulnerability summary
CVE-2021-29657 is a high (CVSS 7.4) vulnerability in linux linux_kernel. EPSS estimates a 0.42% chance of exploitation in the next 30 days, higher than 35.9% of scored vulnerabilities. 2 public exploits are recorded.
Public exploit (reference, Date unknown)
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 4 · Related 1Timeline
- 22-07-2021PublishedVulnerability first disclosed.
- 03-08-2024Last modifiedVulnerability information updated.
Description
arch/x86/kvm/svm/nested.c in the Linux kernel before 5.11.12 has a use-after-free in which an AMD KVM guest can bypass access control on host OS MSRs when there are nested guests, aka CID-a58d9166a756. This occurs because of a TOCTOU race condition associated with a VMCB12 double fetch in nested_svm_vmrun.
CVSS metrics
4 scores · 3 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated7.4HighCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- OSV · DebianEcosystem advisory · calculated7.4HighCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS trend
Probability
0.42%
Chance of exploitation in the next 30 days
Percentile
36%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.42% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
2 foundExploit Reference (bugs.chromium.org)
Maturity: unknown
Exploit Reference (cdn.kernel.org)
Maturity: unknown
Weaknesses
CWE · root cause- CWE-367Time-of-check Time-of-use (TOCTOU) Race ConditionThe product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
- CWE-416Use After FreeThe 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 Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
Affected systems
Known conditions: local access, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu17 products
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.3All versions (No fix recorded)
- linux-azureAll versions (No fix recorded)
- linux-azure-5.3All versions (No fix recorded)
- linux-azure-edgeAll versions (No fix recorded)
Debian1 product
- linux< 5.10.28-1
Linux1 product
- linux_kernel≥ 5.10, < 5.10.28 | ≥ 5.11, < 5.11.12
3 vendors · 19 products
References
11 links- packetstormsecurity.com/files/163324/KVM-nested_svm_vmrun-Double-Fetch.htmlX Refsource MISCThird Party AdvisoryVDB Entry
- bugs.chromium.org/p/project-zero/issues/detail?id=2177X Refsource MISCExploitMailing ListPatchThird Party Advisory
- cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.12X Refsource CONFIRMExploitPatchVendor Advisory
