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CVE-2026-18355

HIGHCVSS 7.5/10EPSS 0.84%

Last modified

CVE-2026-18355 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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. EPSS estimates a 0.84% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1
7.5/10

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Probability
0.84%

55.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
Red HatRed Hat Directory Server 11.7 E4S for RHEL 8All versions
Red HatRed Hat Directory Server 11.9 for RHEL 8All versions
Red HatRed Hat Directory Server 12.2 E4S for RHEL 9All versions
Red HatRed Hat Directory Server 12.4 E4S for RHEL 9All versions
Red HatRed Hat Enterprise Linux 10All versions
Red HatRed Hat Enterprise Linux 10.0 Extended Update SupportAll versions
Red HatRed Hat Enterprise Linux 7 Extended Lifecycle SupportAll versions
Red HatRed Hat Enterprise Linux 8All versions
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update SupportAll versions
Red HatRed Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-OnAll versions
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update SupportAll versions
Red HatRed Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-OnAll versions
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update ServiceAll versions
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP SolutionsAll versions
Red HatRed Hat Enterprise Linux 9All versions
Red HatRed Hat Enterprise Linux 9.2 Update Services for SAP SolutionsAll versions
Red HatRed Hat Enterprise Linux 9.4 Update Services for SAP SolutionsAll versions
Red HatRed Hat Enterprise Linux 9.6 Extended Update SupportAll versions
Red HatRed Hat Directory Server 13.2All versions
Red HatRed Hat Directory Server 12All versions

References

Timeline

Published
Last Modified
Status
Awaiting Analysis

Frequently Asked Questions

What is CVE-2026-18355?
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.
How severe is CVE-2026-18355?
CVE-2026-18355 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.84% probability of exploitation in the next 30 days.
How do I fix CVE-2026-18355?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST