CVE-2023-6992

Service interruption via deflate heap corruption

Published Jan 4, 2024 · Updated Sep 6, 2024

Heap-based buffer overflow in Cloudflare zlib before 8352d10 allows local users to interrupt software through crafted compression input. In deflate.c, longest_match accepts a zero prev_length that causes a heap over-read, while deflate_stored reserves five header bytes even though bi_window can emit six, producing a one-byte heap overflow. The attacker must get the host application to compress crafted local input; the documented consequence is software interruption.

CVSS severity4.0
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in Cloudflare zlib before 8352d10 allows local users to interrupt software through crafted compression input. In deflate.c, longest_match accepts a zero prev_length that causes a heap over-read, while deflate_stored reserves five header bytes even though bi_window can emit six, producing a one-byte heap overflow. The attacker must get the host application to compress crafted local input; the documented consequence is software interruption.

The record

CVE
CVE-2023-6992
Published
Jan 4, 2024
Updated
Sep 6, 2024
Vendor
Cloudflare
Product
Cloudflare zlib
Classifications
CWE-122, CWE-126, CWE-20, T1499.004
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 4, 2024CVE publishedPublication date reported by the CVE source.
  2. Sep 6, 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 <8352d10

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Cloudflare · Cloudflare zlibversion=0 <8352d10

Published CVSS scores

4.0GitHubCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-122Heap-based Buffer Overflow
CWE-126Buffer Over-read
CWE-20Improper Input Validation
T1499.004Application or System Exploitation

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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