CVE-2021-3404Public exploit

Parser crash via undersized version field

Published Mar 4, 2021 · Updated Aug 3, 2024

Heap buffer over-read in Yeraze ytnef 1.9.3 allows attackers to crash the parser by supplying a crafted TNEF file. TNEFVersion passes an undersized version field to SwapWord, which copies two bytes and reads beyond the allocated heap buffer. The demonstrated consequence is an application abort after the crafted file is parsed; code execution is reported but has not been demonstrated publicly.

CVSS severity7.8
High
EPSS probability1.95%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer over-read in Yeraze ytnef 1.9.3 allows attackers to crash the parser by supplying a crafted TNEF file. TNEFVersion passes an undersized version field to SwapWord, which copies two bytes and reads beyond the allocated heap buffer. The demonstrated consequence is an application abort after the crafted file is parsed; code execution is reported but has not been demonstrated publicly.

The record

CVE
CVE-2021-3404
Published
Mar 4, 2021
Updated
Aug 3, 2024
Vendor
Yeraze
Product
ytnef
Classifications
CWE-119, CWE-787, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 4, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=All versions

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Yeraze · ytnefversion=All versions

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/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.

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No observations available

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

Weakness, pattern, technique

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

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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