CVE-2020-1918Network attack vector

Memory disclosure via negative data-URI seek

Published Mar 10, 2021 · Updated Aug 4, 2024

Buffer under-read in Meta Platforms HHVM affected releases allows attackers to read process memory through crafted data-URI seeks. The MemFile::seek method accepted negative SEEK_SET positions and SEEK_END offsets before the buffer, after which readImpl copied bytes from m_data plus the negative cursor. Reachability requires a Hack application to let attacker-controlled input drive these in-memory file operations; disclosure is limited to memory preceding the selected buffer.

CVSS severity7.5
High
EPSS probability1.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer under-read in Meta Platforms HHVM affected releases allows attackers to read process memory through crafted data-URI seeks. The MemFile::seek method accepted negative SEEK_SET positions and SEEK_END offsets before the buffer, after which readImpl copied bytes from m_data plus the negative cursor. Reachability requires a Hack application to let attacker-controlled input drive these in-memory file operations; disclosure is limited to memory preceding the selected buffer.

The record

CVE
CVE-2020-1918
Published
Mar 10, 2021
Updated
Aug 4, 2024
Vendor
Meta Platforms, Inc.
Product
HHVM
Classifications
CWE-127, CWE-125, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 10, 2021CVE 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.57.0 <unspecified
  2. Affected versionversion=4.81.0 <unspecified
  3. Affected versionversion=4.94.0
  4. Affected versionversion=4.95.0
  5. Affected versionversion=4.96.0
  6. Affected versionversion=4.97.0
  7. Affected versionversion=4.98.0
  8. Affected versionversion=unspecified <4.56.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Meta Platforms, Inc. · HHVMversion=4.57.0 <unspecified; version=4.81.0 <unspecified; version=4.94.0; version=4.95.0; version=4.96.0; version=4.97.0; version=4.98.0; version=unspecified <4.56.3

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/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.

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-127Buffer Under-read
CWE-125Out-of-bounds Read
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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