CVE-2026-55971: Apache Thrift: C++ ZLIB heap buffer overflow (write) in THeaderTransport::untransform()
CVE-2026-55971 is a vulnerability in Apache Thrift: C++ ZLIB heap buffer overflow (write) in THeaderTransport::untransform(), rated Important by Microsoft, with a CVSS 3.1 base score of 9.8 (Critical). An attacker can exploit it remotely over the network, without any privileges and without user interaction. Microsoft has not reported exploitation in the wild. The EPSS model estimates a 0.98% probability of exploitation activity in the next 30 days, higher than 63% of all scored vulnerabilities. Microsoft released the fix on 6 August 2026, outside Patch Tuesday. It affects 1 product in 1 product family (Open Source Software).
Key facts
- CVE ID
- CVE-2026-55971
- Severity
- Critical CVSS 9.8
- Microsoft severity
- Important
- Exploited in the wild
- No
- Publicly disclosed
- No
- Weakness
- CWE-122
- EPSS
- 0.98% (percentile 63%)
- CISA KEV
- Not listed
- Released
- Last updated
- Patch Tuesday
- July 2026 Patch Tuesday
- Product families
- Open Source Software
CVSS score and vector
Microsoft scores CVE-2026-55971 at 9.8 (temporal 9.8) using CVSS 3.1. Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
| Metric | Value |
|---|---|
| Attack vector | Network |
| Attack complexity | Low |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality impact | High |
| Integrity impact | High |
| Availability impact | High |
Affected products (1)
Open Source Software
| Product | Security update | Type | Fixed build | Restart |
|---|---|---|---|---|
| azl3 thrift 0.15.0-6 on Azure Linux 3.0 | CBL-Mariner Releases | Security Update | 0.24.0-1 | No |
NIST NVD data
- NVD status
- Analyzed
- NVD CVSS
- 9.8 (CRITICAL)
- NVD weakness
- CWE-122
- Published to NVD
- NVD last modified
Affected configurations (CPE)
| Product | Vulnerable versions |
|---|---|
| thrift | before 0.24.0 |
References
- https://lists.apache.org/thread/7v3jhgwfbmhx42424phydlnzb109g8b9 (Release Notes)
- https://lists.apache.org/thread/xjs36m6kjxpmrmzwck636msg3nvoqnmx (Vendor Advisory)
- http://www.openwall.com/lists/oss-security/2026/07/24/42 (Mailing List, Third Party Advisory)
Revision history
| Version | Date | Description |
|---|---|---|
| 1.0 | Information published. |