CVE-2025-6499Public exploit

Local crash via multiline terminator bounds error

Published Jun 23, 2025 · Updated Jun 23, 2025

Heap-buffer over-read in Vsevolod Stakhov libucl 0.9.0 through 0.9.2 allows local users to crash a parsing process via crafted UCL. The multiline terminator check accepts a remaining buffer exactly as long as the terminator, then reads p[term_len] one byte past the heap allocation. Reaching the fault requires a local user to supply crafted multiline UCL to a process that parses it; the demonstrated consequence is process termination under AddressSanitizer.

CVSS severity3.3
Low
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-buffer over-read in Vsevolod Stakhov libucl 0.9.0 through 0.9.2 allows local users to crash a parsing process via crafted UCL. The multiline terminator check accepts a remaining buffer exactly as long as the terminator, then reads p[term_len] one byte past the heap allocation. Reaching the fault requires a local user to supply crafted multiline UCL to a process that parses it; the demonstrated consequence is process termination under AddressSanitizer.

The record

CVE
CVE-2025-6499
Published
Jun 23, 2025
Updated
Jun 23, 2025
Vendor
Vsevolod Stakhov
Product
libucl
Classifications
CWE-119, CWE-787, CWE-122, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 23, 2025CVE publishedPublication date reported by the CVE source.
  2. Jun 23, 2025Record 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=0.9.0
  2. Affected versionversion=0.9.1
  3. Affected versionversion=0.9.2

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Vsevolod Stakhov · libuclversion=0.9.0; version=0.9.1; version=0.9.2

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
1.9VulDBCVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
3.3VulDBCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
1.7VulDBAV:L/AC:L/Au:S/C:N/I:N/A:P

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-787Out-of-bounds Write
CWE-122Heap-based Buffer Overflow
T1499.004Application or System Exploitation

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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