CVE-2026-121996
Description
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.
Statement
This flaw is present in gdbserver as shipped with Red Hat Enterprise Linux. An attacker with network access to an exposed gdbserver port can exploit this without authentication or user interaction to disclose heap memory contents or crash gdbserver.
Mitigation
There is no mitigation for this vulnerability. gdbserver has no authentication mechanism; exposure is limited only by network access to the gdbserver port.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.2 | N/A | 8.2 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | Low | N/A | Low |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
Red Hat CVSS v3 Score Explanation
C:L for heap address disclosure (ASLR-defeating leak). A:H for deterministic crash via wild pointer (*actparm advanced by full declared xlen regardless of actual data). Note: analysis.md scored this 5.3 (A:N) omitting the crash path; corrected to 7.5 based on primary bug report confirming A:H. Flagged for human review.
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
If the dereferencing operation is for a read, then the attack might allow reading of sensitive data, cause a crash, or set a variable to an unexpected value (since the value will be read from an unexpected memory location).
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If the untrusted pointer references a memory location that is not accessible to the product, or points to a location that is "malformed" or larger than expected by a read or write operation, the application may terminate unexpectedly.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands; Modify Memory
If the pointer is dereferenced for a write operation, the attack might allow modification of critical state variables, cause a crash, or execute code. If the untrusted pointer is used in a function call, then the attacker might be able to call arbitrary functions.
Acknowledgements
Red Hat would like to thank Pulkit Singh Singaria for reporting this issue.
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