CVE-2021-3889Network attack vector

Memory disclosure or crash via malformed Huffman data

Published Oct 19, 2021 · Updated Aug 3, 2024

Out-of-bounds read in libmobi's Huffman decompressor before 0.8 allows attackers to expose memory or crash a consumer via a crafted MOBI file. In mobi_decompress_huffman_internal(), code_length was incremented without checking the 33-entry mincode and maxcode table boundary before another lookup. A victim must cause a consuming application to parse the crafted ebook, after which the invalid read exposes process memory or terminates the process.

CVSS severity8.1
High
EPSS probability1.29%
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 read in libmobi's Huffman decompressor before 0.8 allows attackers to expose memory or crash a consumer via a crafted MOBI file. In mobi_decompress_huffman_internal(), code_length was incremented without checking the 33-entry mincode and maxcode table boundary before another lookup. A victim must cause a consuming application to parse the crafted ebook, after which the invalid read exposes process memory or terminates the process.

The record

CVE
CVE-2021-3889
Published
Oct 19, 2021
Updated
Aug 3, 2024
Vendor
bfabiszewski
Product
libmobi
Classifications
CWE-119, CWE-823, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 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=unspecified <0.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

bfabiszewski · libmobiversion=unspecified <0.8

Published CVSS scores

5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:N/A:P
8.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H
7.1huntr.devCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-823Use of Out-of-range Pointer Offset
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

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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