CVE-2021-37311Public exploitNetwork attack vector

Service crash via incorrect SignalBase downcast

Published Feb 3, 2023 · Updated Mar 26, 2025

Buffer overflow in Fcitx 5 5.0.8 allows remote attackers to crash the input method service via a crafted message to its listening port. SignalAdaptor incorrectly downcasts SignalBase to a Signal specialization with the wrong combiner, producing an indeterminate CheckUpdateResult and a DBus assertion failure. No authentication or user interaction is required, and the documented consequence is a service crash rather than data disclosure or code execution.

CVSS severity7.5
High
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Buffer overflow in Fcitx 5 5.0.8 allows remote attackers to crash the input method service via a crafted message to its listening port. SignalAdaptor incorrectly downcasts SignalBase to a Signal specialization with the wrong combiner, producing an indeterminate CheckUpdateResult and a DBus assertion failure. No authentication or user interaction is required, and the documented consequence is a service crash rather than data disclosure or code execution.

The record

CVE
CVE-2021-37311
Published
Feb 3, 2023
Updated
Mar 26, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 3, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 26, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499Endpoint Denial of Service

Public exploit references

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo