CVE-2026-11610
Description
A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base). After a successful SASL bind with integrity protection (SSF > 0), an authenticated attacker can send a specially crafted oversized LDAP UNBIND packet that is copied into a 512-byte heap receive buffer without a bounds check in sasl_io_recv() in sasl_io.c. This allows up to approximately 2 megabytes of attacker-controlled data to overflow the buffer, causing a denial of service (server crash). In FreeIPA and Red Hat Identity Management deployments, any domain user with a valid Kerberos ticket, any enrolled host, or any service account can trigger this vulnerability over the network after authenticating via GSSAPI. The vulnerable code path has existed since approximately 2013 (389-ds-base 1.3.2) and was not addressed by the CVE-2025-14905 fix, which patched a separate heap overflow in schema.c only.
Statement
Red Hat rates this issue as Important impact. After a successful SASL bind with integrity protection (SSF > 0), an authenticated remote attacker can send a crafted oversized LDAP UNBIND packet that is copied into a 512-byte heap receive buffer without a bounds check in sasl_io_recv(). Up to roughly two megabytes of attacker-controlled data can overflow the buffer, reliably crashing ns-slapd on production builds. Exploitation requires a valid SASL-authenticated LDAP session, not Directory Manager access. Any user who can bind with SASL mechanisms such as GSSAPI/Kerberos or DIGEST-MD5 can trigger the denial of service. In deployments where domain users, enrolled hosts, and service accounts routinely authenticate to the directory over Kerberos, the attack surface includes any such principal with network access to LDAP. This flaw is independent of CVE-2025-14905, which patched a separate heap overflow in schema.c and did not modify sasl_io.c.
Mitigation
There is no complete workaround for this flaw.
Mitigations that reduce exposure:
1. Restrict network access to LDAP ports (389/636) to trusted networks only.
Note: In FreeIPA/IdM deployments, enrolled clients require LDAP access and
this may not be practical.
2. If DIGEST-MD5 is not required, disable it via nsslapd-allowed-sasl-mechanisms
in cn=config. GSSAPI/Kerberos cannot be disabled in FreeIPA/IdM without breaking
domain authentication.
3. Monitor for oversized LDAP UNBIND packets (standard UNBIND is 7 bytes; alert on
UNBIND packets exceeding ~100 bytes).
4. Lowering nsslapd-maxbersize reduces maximum overflow size but does not eliminate
the vulnerability.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.8 | N/A | 8.8 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | Low | N/A | Low |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
Integrity,Confidentiality,Availability,Access Control
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Modify Memory
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. Besides important user data, heap-based overflows can be used to overwrite function pointers that may be living in memory, pointing it to the attacker's code. Even in applications that do not explicitly use function pointers, the run-time will usually leave many in memory. For example, object methods in C++ are generally implemented using function pointers. Even in C programs, there is often a global offset table used by the underlying runtime.
Integrity,Confidentiality,Availability,Access Control,Other
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Other
When the consequence is arbitrary code execution, this can often be used to subvert any other security service.
Acknowledgements
This issue was discovered by Ian Murphy (Red Hat).
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