CVE-2018-18688Public exploitNetwork attack vector

Signature bypass via unsigned incremental PDF updates

Published Jan 7, 2021 · Updated Aug 5, 2024

Improper signature verification in multiple PDF readers allows attackers to present altered pages as covered by a valid signature. Signature-validation logic verifies the original signed byte range, while incremental updates append body objects that readers display without identifying them as unsigned changes. Exploitation requires a recipient to open and validate a crafted signed PDF and trust its signing certificate, after which added pages or annotations appear authentic.

CVSS severity5.3
Medium
EPSS probability1.13%
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 multiple PDF readers allows attackers to present altered pages as covered by a valid signature. Signature-validation logic verifies the original signed byte range, while incremental updates append body objects that readers display without identifying them as unsigned changes. Exploitation requires a recipient to open and validate a crafted signed PDF and trust its signing certificate, after which added pages or annotations appear authentic.

The record

CVE
CVE-2018-18688
Published
Jan 7, 2021
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-347
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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

5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature

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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