CVE-2021-40326Public exploit

Arbitrary file write via unvalidated incremental PDF data

Published Aug 29, 2022 · Updated Aug 4, 2024

Improper signature verification in Foxit PDF Reader and Editor before 11.1 and PhantomPDF before 10.1.6 allows attackers to alter displayed content. A crafted incremental update changes the trailer's cross-reference offset to reveal pre-positioned hidden content, which the verifier accepts without invalidating the signature. A victim must open the attacker-modified signed PDF; the technique can also trigger an arbitrary file write during verification.

CVSS severity5.5
Medium
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper signature verification in Foxit PDF Reader and Editor before 11.1 and PhantomPDF before 10.1.6 allows attackers to alter displayed content. A crafted incremental update changes the trailer's cross-reference offset to reveal pre-positioned hidden content, which the verifier accepts without invalidating the signature. A victim must open the attacker-modified signed PDF; the technique can also trigger an arbitrary file write during verification.

The record

CVE
CVE-2021-40326
Published
Aug 29, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-347, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 29, 2022CVE 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 vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

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-347Improper Verification of Cryptographic Signature
T1204.002Malicious File

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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