CVE-2021-28667Network attack vector

Service hang via repeated Unicode decoding

Published Mar 18, 2021 · Updated Aug 3, 2024

Denial of service in StackStorm before 3.4.1 allows remote attackers to exhaust CPU, memory, and disk via logged Unicode data. The stderr-to-logger routing code repeatedly retries a failed UTF-8-to-ASCII decode instead of stopping after the first exception. Exploitation requires Python 3, a non-UTF-8 service locale, and attacker-controlled Unicode data that reaches a log path, causing the affected service to hang while its log grows.

CVSS severity7.5
High
EPSS probability2.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in StackStorm before 3.4.1 allows remote attackers to exhaust CPU, memory, and disk via logged Unicode data. The stderr-to-logger routing code repeatedly retries a failed UTF-8-to-ASCII decode instead of stopping after the first exception. Exploitation requires Python 3, a non-UTF-8 service locale, and attacker-controlled Unicode data that reaches a log path, causing the affected service to hang while its log grows.

The record

CVE
CVE-2021-28667
Published
Mar 18, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 18, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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 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
7.1NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:C

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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