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CVE-2026-12549 Red Hat CVE debrief

CVE-2026-12549 is a vulnerability caused by a regression in the fix for CVE-2026-2443. A subsequent rework commit replaced specific overflow checks with a general signed comparison, leading to improper clamping of negative start values when a client sends a Range request with a suffix length exceeding the content size. This results in malformed HTTP 206 responses and log flooding. The vulnerability has a CVSS score of 4.8 and is classified as MEDIUM severity. The CVE was published on 2026-06-22T16:16:34.090Z and last modified on 2026-06-23T15:16:33.000Z.

Vendor
Red Hat
Product
Red Hat Enterprise Linux 10
CVSS
MEDIUM 4.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-22
Original CVE updated
2026-07-08
Advisory published
2026-06-22
Advisory updated
2026-07-08

Who should care

Defenders of web applications and services that use Range requests should be aware of this vulnerability. Although the affected product is not specified, the presence of Red Hat references suggests that users of Red Hat products may need to take action. Organizations using web servers or services that support Range requests should review their configurations and monitor for potential exploitation.

Technical summary

The vulnerability arises from a regression in the fix for CVE-2026-2443, where specific overflow checks were replaced with a general signed comparison. When a client sends a Range request with a suffix length exceeding the content size, the resulting negative start value is not properly clamped. This leads to malformed HTTP 206 responses and log flooding. The issue can be triggered by a client sending a specially crafted Range request.

Defensive priority

Defenders should prioritize reviewing and updating configurations for web servers or services that support Range requests. They should also monitor logs for signs of potential exploitation and implement compensating controls to detect and prevent similar attacks.

Recommended defensive actions

  • Review and update configurations for web servers or services that support Range requests.
  • Monitor logs for signs of potential exploitation.
  • Implement compensating controls to detect and prevent similar attacks.
  • Inventory and assess web applications and services for potential exposure.
  • Consider implementing additional security measures, such as web application firewalls or intrusion detection systems.

Evidence notes

The CVE record and NVD detail provide official information about the vulnerability. Red Hat references suggest that users of Red Hat products may need to take action. However, the affected product is not specified, and further investigation is needed to determine the scope of potential impact.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-12549 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-12549

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-12549 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-12549

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.