CVE-2021-45931Public exploitNetwork attack vector

Application crash via inconsistent set state

Published Dec 31, 2021 · Updated Aug 4, 2024

Out-of-bounds write in unreleased HarfBuzz commits allows context-dependent attackers to crash applications that process crafted font data. hb_bit_set_invertible_t::set copied the inverted flag after its backing set entered an allocation-error state, leaving inconsistent metadata that later caused an out-of-bounds write. Debian and Red Hat found that the faulty code was introduced and fixed between the 2.9.0 and 2.9.1 releases, so no released HarfBuzz version was affected.

CVSS severity6.5
Medium
EPSS probability1.78%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in unreleased HarfBuzz commits allows context-dependent attackers to crash applications that process crafted font data. hb_bit_set_invertible_t::set copied the inverted flag after its backing set entered an allocation-error state, leaving inconsistent metadata that later caused an out-of-bounds write. Debian and Red Hat found that the faulty code was introduced and fixed between the 2.9.0 and 2.9.1 releases, so no released HarfBuzz version was affected.

The record

CVE
CVE-2021-45931
Published
Dec 31, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 31, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
6.5CanonicalCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
7.5SUSECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P

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

Weakness, pattern, technique

CWE-787Out-of-bounds Write
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

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Your stack

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