CVE-2024-53863Network attack vector

External decoder invocation via unrestricted image thumbnailing

Published Dec 3, 2024 · Updated Dec 3, 2024

Unsafe image processing in Element HQ Synapse before 1.120.1 allows remote attackers to invoke external decoders through thumbnail requests. The Thumbnailer constructor passes the stored media path to Pillow Image.open without a format allowlist, enabling uncommon codecs and helpers such as Ghostscript. Reachability requires dynamic thumbnailing or a specially crafted request; the direct downstream decoder consequence is unspecified.

CVSS severity8.2
High
EPSS probability0.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unsafe image processing in Element HQ Synapse before 1.120.1 allows remote attackers to invoke external decoders through thumbnail requests. The Thumbnailer constructor passes the stored media path to Pillow Image.open without a format allowlist, enabling uncommon codecs and helpers such as Ghostscript. Reachability requires dynamic thumbnailing or a specially crafted request; the direct downstream decoder consequence is unspecified.

The record

CVE
CVE-2024-53863
Published
Dec 3, 2024
Updated
Dec 3, 2024
Vendor
Element HQ
Product
Synapse
Classifications
CWE-434, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 3, 2024CVE publishedPublication date reported by the CVE source.
  2. Dec 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=0 <1.120.1
  2. Affected versionversion=< 1.120.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Element HQ · Synapseversion=0 <1.120.1; version=< 1.120.1

Published CVSS scores

8.2GitHub CNACVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA: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 exploitUnconfirmed

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
T1190Exploit Public-Facing Application

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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