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Out-of-bounds ReadWeakness · CWE-125

CVE-2026-50643

MEDIUM · 5.1 CVSS v4.0 Published 2026-06-18
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
56/100
Remediation priority · Elevated
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
8cc is vulnerable to an Out‑of‑Bounds Read due to improper handling of #line directives and GNU linemarkers. The compiler accepts attacker-controlled filename and line number metadata and later uses it without validation when accessing source line arrays. By supplying invalid or oversized line numbers, an attacker can trigger out-of-bounds memory access and a crash. Maintainer of this project was notified early about this vulnerability, but didn't respond with the details of vulnerability or vulnerable version range. Version corresponding to the commit b480958 was tested and confirmed as vulnerable, other versions were not tested but might also be vulnerable.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The 8cc compiler has an out-of-bounds read vulnerability in its handling of #line directives and GNU linemarkers. The compiler accepts attacker-controlled filename and line number metadata without validation and later uses this metadata to index into source line arrays. By supplying invalid or oversized line numbers, an attacker can trigger out-of-bounds memory access and cause a denial of service via crash.

MitigationImplement bounds checking on line number metadata from #line directives and GNU linemarkers before accessing source line arrays. Validate that line numbers fall within the actual source file bounds and reject or sanitize invalid metadata.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify if 8cc compiler is installed
    Run 'which 8cc' or 'command -v 8cc' to locate the 8cc binary on the system
    Affected if 8cc binary exists on the system - the compiler is present and could be used to compile untrusted source code
  2. Determine the installed version of 8cc
    Run '8cc --version' or '8cc -v' to retrieve the version string. If version output is unavailable, check for package manager installation details via 'dpkg -l 8cc' or 'rpm -qi 8cc'
    Affected if The installed version cannot be confirmed as a patched version - without a reported fixed version, any installed 8cc may be affected
  3. Inspect source code processing of #line directives
    If source code is available, examine the parser handling of #line directives and GNU linemarkers (lines starting with # followed by digits). Look for code that extracts line numbers from these directives without bounds validation before array access
    Affected if The compiler processes #line directives and uses the extracted line numbers to index into source line arrays without validating that the line numbers fall within the actual source file bounds
  4. Test for vulnerable behavior with crafted input
    Create a test source file containing a #line directive with an extremely large line number (e.g., '#line 999999999') followed by code that triggers source line array access, then compile it with 8cc and observe for crashes or abnormal behavior
    Affected if The compiler crashes, segfaults, or exhibits out-of-bounds memory access when processing #line directives with invalid line numbers - this confirms the vulnerability is present and triggerable

A system is affected if 8cc is installed and processes #line directives or GNU linemarkers without validating that attacker-supplied line numbers are within the actual source file bounds before using them to index source line arrays.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Implement bounds checking on line number metadata from #line directives and GNU linemarkers before accessing source line arrays. Validate that line numbers fall within the actual source file bounds and reject or sanitize invalid metadata.

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-50643 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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