CVE-2021-40506

Execution corruption via stale overflow flag

Published Apr 18, 2023 · Updated Feb 6, 2025

Core and compute flaw in OpenRISC OR1200 2011-09-10 through 2015-11-11 allows context-dependent attackers to corrupt execution. The always block in rtl/verilog/or1200_alu.v updates the overflow bit only for add and subtract operations, leaving a stale flag after MSB and MAC instructions. Software must execute an affected instruction and then rely on the flag in a data or control path, causing incorrect computation or control flow.

CVSS severity9.8
Critical
EPSS probability0.73%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Core and compute flaw in OpenRISC OR1200 2011-09-10 through 2015-11-11 allows context-dependent attackers to corrupt execution. The always block in rtl/verilog/or1200_alu.v updates the overflow bit only for add and subtract operations, leaving a stale flag after MSB and MAC instructions. Software must execute an affected instruction and then rely on the flag in a data or control path, causing incorrect computation or control flow.

The record

CVE
CVE-2021-40506
Published
Apr 18, 2023
Updated
Feb 6, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-287, CWE-1201
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Apr 18, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 6, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
CWE-1201Core and Compute Issues

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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