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Fencer Intel
high 7.8

CVE-2021-3404 json

In ytnef 1.9.3, the SwapWord function in lib/ytnef.c allows remote attackers to cause a denial-of-service (and potentially code execution)…

published 5y ago modified 4mo ago also EUVD-2021-26732

cvss
7.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.9%
EPSS 1.9% chance of exploitation in 30 days, percentile 80%
public exploits
0
none known

Summary

In ytnef 1.9.3, the SwapWord function in lib/ytnef.c allows remote attackers to cause a denial-of-service (and potentially code execution) due to a heap buffer overflow which can be triggered via a crafted file.

Patch / fix

  • libytnef Debian 14, Debian 13, Debian 12 1.9.3-3

debian advisories DEBIAN-CVE-2021-3404

  • ytnef Alpine 3.24, Alpine 3.23, Alpine 3.22 +9 more 1.9.3-r1

alpine advisories ALPINE-CVE-2021-3404

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libytnef Arch Linux 1:1.9.3-1

arch linux advisories AVG-1552

Is CVE-2021-3404 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3404 updated cvss 5.5

ytnef: heap-based buffer overflow in SwapWord function in lib/ytnef.c via crafted file

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.94% chance of exploitation in the next 30 days, higher than 80% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/Yeraze/ytnef/issues/86 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P

Affected products

  • n/a ytnef

Classification

Weakness
  • CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer
  • CWE-787 Out-of-bounds Write

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.