# CVE-2026-121996: Gdb: gdbserver: heap disclosure and wild pointer in gdb_parse_agent_expr via untrusted agent-expression length

Status: published. Published: 2026-11-05. Updated: 2026-11-06.

A length validation flaw in gdbserver's agent-expression parser allows an unauthenticated remote attacker to read uninitialized heap memory from the gdbserver process and cause a denial of service. Disclosed heap content includes addresses suitable for defeating ASLR in further exploitation.

## Remediation

- workaround: There is no mitigation for this vulnerability. gdbserver has no authentication mechanism; exposure is limited only by network access to the gdbserver port.

--- CME Mitigation Guidance (2026-11-06) ---
Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.

The highest-value action is to restrict network access to exposed gdbserver listening ports and eliminate untrusted agent-expression length handling in gdbserver: upgrade to the corresponding fixed Red Hat builds, which apply the documented input check, closing crafted agent-expression packet with declared length exceeding actual payload data. Until patched, this is a concern on Linux systems hosting gdbserver with an exposed listening port, so Restrict network access to the gdbserver listening port using host or network firewalls, limiting connectivity to trusted debugging clients only. As a compensating measure, Maintain SELinux in enforcing mode to confine the gdbserver process domain and limit host impact if heap disclosures are used to stage subsequent code execution. These controls limit blast radius and contain exploitation, but they do not fix the underlying length validation defect — apply the upstream patch to fully remediate.

Highest-impact CME: CME-301 SELinux (Enforcing Mode) (medium) (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (crash): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10 (gdb): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (gdb): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (gdb): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (crash): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (gcc-toolset-14-gdb): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (gcc-toolset-15-gdb): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (gdb): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (crash): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (gdb): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Hardened Images (gdb): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 8.2 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H; source: CNA: redhat

- CVSS 3.1: 8.2 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H; source: NVD: secalert@redhat.com

- CISA KEV: No listing in collected sources

- EPSS: 0.47% as of 2026-11-06; percentile 40.90%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-822

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/security/cve/CVE-2026-121996 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2565678 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-121996 (secalert@redhat.com)

- https://bugzilla.redhat.com/show_bug.cgi?id=2565678 (secalert@redhat.com)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-121996; retrieved 2026-11-06; source updated 2026-11-06

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-121996; retrieved 2026-11-06; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-121996; retrieved 2026-11-06; source updated Not reported

Revision: 60697c7808bc4b393eeabd35ad2db73d961e373f661703d412c0d263910c5a5b

Canonical: https://y2.dev/cve/CVE-2026-121996

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.