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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Obtain valid LDAP bind credential
  2. Delivery
    Initiate SASL GSSAPI/DIGEST-MD5 bind with integrity protection (SSF > 0)
  3. Exploit
    Send crafted SASL record with wire-format length of 0-2 bytes
  4. Execution
    Unsigned integer underflow inflates PR_Recv read-size to ~4 GiB
  5. Persist
    Heap buffer overflow with attacker-controlled data overwrites slapd heap
  6. Impact
    Crash (DoS) or arbitrary code execution as slapd process user

Vulnerability Assessment

Weakness
CWE
CWE-191
ASVS 5.0
V15 - Secure Coding and Architecture Integer underflow checks
Exploitation Conditions

Exploitation requires three concrete preconditions: (1) a valid LDAP bind credential for any user account in the directory, consistent with PR:L - no administrative privilege is needed; (2) the attacker must complete a SASL bind with integrity or privacy protection negotiated (SSF > 0), meaning the SASL mechanism used must support and activate an integrity layer - GSSAPI with Kerberos (the FreeIPA/IdM default), SASL DIGEST-MD5 with integrity, or similar; and (3) network connectivity to the 389-ds LDAP port (default 389/636). Deployments that enforce SSF=0 globally or restrict all SASL mechanisms to those without integrity layers would not be reachable via this code path. There is no requirement for local system access, elevated OS privilege, or a specific operating system configuration beyond the SASL session establishment.
Impact

The Red Hat-assigned CVSS 3.1 vector (AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H, score 7.5) is consistent with the exploitation conditions: network-accessible, no user interaction required, but gated behind both a valid LDAP credential and an SSF > 0 SASL session (AC:H, PR:L). The heap overflow is filled with attacker-controlled network content, making RCE technically plausible rather than theoretical. No EPSS score was provided; no KEV listing and no public exploit code have been identified at time of analysis. The practical attacker barrier is meaningful - any exploit must first obtain LDAP bind credentials and negotiate SASL with integrity protection - but in enterprise environments where service accounts routinely hold LDAP read access and GSSAPI/Kerberos is the default authentication mechanism, this bar may not be high. The prior incomplete fix (CVE-2026-11774) suggests the root cause was partially misunderstood, which may delay patch awareness among operators. Priority should be elevated for RHEL Identity Management or FreeIPA deployments where 389-ds is reachable from untrusted segments.
Exploit ScenarioDerived

An attacker holding any valid LDAP bind credential - such as a compromised service account or a Kerberos ticket in a FreeIPA environment - authenticates to 389 Directory Server using SASL GSSAPI with integrity protection, establishing an SSF > 0 session. The attacker then sends a crafted SASL-wrapped record with a wire-format length of 1 byte, causing the integer underflow that inflates the PR_Recv read-size to ~4 GiB and overwrites approximately 4 GiB of heap memory with attacker-controlled network data. Depending on heap layout, this results in an immediate server crash (denial of service) or, with heap-shaping techniques, arbitrary code execution as the directory server process user.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.8% exploitation probability (EPSS)

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AnalysisAIv1 – Sep 07, 2026

Heap buffer overflow in 389 Directory Server's SASL I/O layer allows a remote authenticated attacker to crash the server or potentially execute arbitrary code. The root cause is an integer underflow in sasl_io_read_packet(): a crafted SASL record with a wire-format length of 0, 1, or 2 bytes causes an unsigned subtraction to wrap around, instructing PR_Recv to read approximately 4 GiB of attacker-controlled network data into a 1024-byte heap buffer. The flaw is explicitly distinct from CVE-2026-11774, whose patch addressed only upper-bound validation, leaving the lower-bound path unguarded. No public exploit code or CISA KEV listing has been identified at time of analysis.

RemediationAI

Apply the updated 389-ds-base RPM errata from Red Hat via dnf update 389-ds-base once errata are published; monitor https://access.redhat.com/security/cve/CVE-2026-18355 and the associated Bugzilla entry (2509186) for the exact patched package version, which had not been confirmed in available data at time of analysis. As an interim network-level control, restrict LDAP port 389 (and LDAPS 636) access to trusted internal subnets using firewall rules to limit which hosts can initiate SASL binds; this does not eliminate risk from malicious insiders or compromised internal hosts but raises the attacker's access barrier. Disabling SASL integrity and privacy protection (forcing SSF=0) would prevent exploitation of this specific code path but strips transport-layer security from LDAP traffic, making it an unacceptable compensating control in most deployments. Enabling 389-ds core dump capture and monitoring for unexpected slapd process crashes can serve as a detection signal for exploitation attempts.

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Technical ContextAI · show details

389 Directory Server (389-ds-base) is the open-source LDAP server underlying Red Hat Directory Server and FreeIPA/IdM. The vulnerable component is the SASL (Simple Authentication and Security Layer) I/O layer. After a client completes a SASL bind with integrity or privacy protection (Security Strength Factor SSF > 0, e.g., via GSSAPI/Kerberos or DIGEST-MD5), subsequent LDAP traffic is wrapped in SASL-encoded records. In sasl_io_start_packet(), the wire-format record length is validated only against an upper bound. A small length value (0, 1, or 2) causes encrypted_buffer_count to fall below the already-consumed encrypted_buffer_offset, triggering a CWE-191 unsigned integer underflow. The resulting ~4 GiB computed read-size is passed to NSPR's PR_Recv, which writes far beyond the 1024-byte heap buffer with attacker-controlled content. Affected CPEs span Red Hat Directory Server 11, 12, and 13 (cpe:2.3:a:red_hat:red_hat_directory_server_11/12/13) and 389-ds-base as shipped in RHEL 6 through RHEL 10.

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Severity by source

Vendor (redhat) PRIMARY 7.5 HIGH
AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
vuln.today AI 7.5 HIGH

Network-reachable LDAP service requires an authenticated SASL bind with SSF > 0 before the vulnerable path is accessible, justifying PR:L and AC:H; heap overflow with attacker-controlled content supports C:H/I:H/A:H.

3.1 AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
4.0 AV:N/AC:H/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
SUSE HIGH
Red Hat 7.5 HIGH

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionCVE.org

A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base). In sasl_io_start_packet(), the wrapped-record length read from the wire is validated only against an upper bound. A small wire length (0, 1, or 2) produces an encrypted_buffer_count below the already-consumed encrypted_buffer_offset, causing an unsigned subtraction underflow in sasl_io_read_packet(). PR_Recv is then requested to read approximately 4 GiB into a 1024-byte heap buffer, resulting in a heap buffer overflow with attacker-controlled content. After a successful SASL bind with integrity protection (SSF > 0), a remote authenticated attacker can cause a denial of service or potentially achieve remote code execution. This flaw is distinct from CVE-2026-11774, whose fix only guards against upper-bound overflow.

Executive ViewAI

Why It Matters

389 Directory Server deployments are vulnerable to a heap buffer overflow in the SASL authentication layer that allows authenticated users to crash the directory service or potentially execute code with server privileges. Directory servers are critical infrastructure for enterprise user authentication and authorization; compromise or unavailability cascades across dependent applications and systems. With no vendor patch currently available, organizations face elevated operational risk during an unpatched window and should implement immediate isolation and monitoring measures.

Business Impact: High
Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations: (1) Network segmentation-restrict directory server to authorized administrative and system clients only, block untrusted network paths; (2) Disable SASL authentication if operationally feasible and fallback authentication mechanisms exist; (3) Implement connection-rate limiting and anomaly detection on SASL sessions; (4) Deploy directory server on isolated network segment with egress filtering to trusted systems only; (5) Maintain current backups and test failover procedures to secondary directory infrastructure.

Threat Intelligence Overview

EPSS Score
0.8%
Top 45% exploitable
Prevalence
Medium
standard LDAP server in RHEL and FreeIPA enterprise deployments
Data Quality
6 sources
Confidence: High
EUVD NVD CVE.org EPSS Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.8%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
No
Human Impact
High

Priority Score

39
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +38
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Integer Overflow MEDIUM

Integer overflow occurs when an arithmetic operation produces a result that exceeds the maximum value a given integer type can store.

Remote Code Execution CRITICAL

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

Denial of Service MEDIUM

Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.

Affected Products (CPE)CVE.org

cpe:2.3:a:red_hat:red_hat_directory_server_11:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_directory_server_12:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_directory_server_13:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_10:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_6:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_7:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_8:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_9:*:*:*:*:*:*:*:*

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Same weakness CWE-191 – Integer Underflow

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Liberty Linux 8 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected
SUSE Linux Enterprise Server 16.0 Affected
SUSE Linux Enterprise Server 16.1 Affected

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-18355 ADVISORY https://vuldb.com/vuln/399605 REF https://access.redhat.com/errata/RHSA-2026:64771 REF https://access.redhat.com/errata/RHSA-2026:64776 REF https://access.redhat.com/errata/RHSA-2026:64778 REF https://access.redhat.com/errata/RHSA-2026:64779 REF https://access.redhat.com/errata/RHSA-2026:64780 REF https://access.redhat.com/errata/RHSA-2026:64781 REF https://access.redhat.com/errata/RHSA-2026:64783 REF https://access.redhat.com/errata/RHSA-2026:64784 REF https://access.redhat.com/errata/RHSA-2026:64785 REF https://access.redhat.com/errata/RHSA-2026:64789 REF https://access.redhat.com/errata/RHSA-2026:64790 REF https://access.redhat.com/errata/RHSA-2026:64791 REF https://access.redhat.com/errata/RHSA-2026:64792 REF https://access.redhat.com/errata/RHSA-2026:64793 REF https://access.redhat.com/errata/RHSA-2026:64804 REF https://access.redhat.com/errata/RHSA-2026:65119 REF https://access.redhat.com/errata/RHSA-2026:79217 REF https://access.redhat.com/security/cve/CVE-2026-18355 REF https://bugzilla.redhat.com/show_bug.cgi?id=2509186

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