CVE-2026-5928
Potential buffer under-read in ungetwc
Description
Calling the ungetwc function on a FILE stream with wide characters encoded in a character set that has overlaps between its single byte and multi-byte character encodings, in the GNU C Library version 2.43 or earlier, may result in an attempt to read bytes before an allocated buffer, potentially resulting in unintentional disclosure of neighboring data in the heap, or a program crash. A bug in the wide character pushback implementation (_IO_wdefault_pbackfail in libio/wgenops.c) causes ungetwc() to operate on the regular character buffer (fp->_IO_read_ptr) instead of the actual wide-stream read pointer (fp->_wide_data->_IO_read_ptr). The program crash may happen in cases where fp->_IO_read_ptr is not initialized and hence points to NULL. The buffer under-read requires a special situation where the input character encoding is such that there are overlaps between single byte representations and multibyte representations in that encoding, resulting in spurious matches. The spurious match case is not possible in the standard Unicode character sets.
INFO
Published Date :
April 20, 2026, 9:16 p.m.
Last Modified :
April 23, 2026, 3:33 p.m.
Remotely Exploit :
Yes !
Source :
3ff69d7a-14f2-4f67-a097-88dee7810d18
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
Solution
- Update GNU C Library to a fixed version.
- Avoid using ungetwc on affected FILE streams.
- Review character encoding handling in applications.
Public PoC/Exploit Available at Github
CVE-2026-5928 has a 1 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-5928.
| URL | Resource |
|---|---|
| https://sourceware.org/bugzilla/show_bug.cgi?id=33998 | Exploit Issue Tracking |
| https://sourceware.org/bugzilla/show_bug.cgi?id=33998 | Exploit Issue Tracking |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-5928 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-5928
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
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Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-5928 vulnerability anywhere in the article.
-
Daily CyberSecurity
Three Silent Vulnerabilities Discovered in the glibc Core
The core of many Linux-based operating systems is facing a series of security challenges. Recent advisories for the GNU C Library (glibc) have disclosed three distinct vulnerabilities ranging from hea ... Read more
The following table lists the changes that have been made to the
CVE-2026-5928 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Apr. 23, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:gnu:glibc:*:*:*:*:*:*:*:* versions up to (including) 2.43 Added Reference Type CISA-ADP: https://sourceware.org/bugzilla/show_bug.cgi?id=33998 Types: Exploit, Issue Tracking Added Reference Type GNU C Library: https://sourceware.org/bugzilla/show_bug.cgi?id=33998 Types: Exploit, Issue Tracking -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Apr. 21, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added Reference https://sourceware.org/bugzilla/show_bug.cgi?id=33998 -
New CVE Received by 3ff69d7a-14f2-4f67-a097-88dee7810d18
Apr. 20, 2026
Action Type Old Value New Value Added Description Calling the ungetwc function on a FILE stream with wide characters encoded in a character set that has overlaps between its single byte and multi-byte character encodings, in the GNU C Library version 2.43 or earlier, may result in an attempt to read bytes before an allocated buffer, potentially resulting in unintentional disclosure of neighboring data in the heap, or a program crash. A bug in the wide character pushback implementation (_IO_wdefault_pbackfail in libio/wgenops.c) causes ungetwc() to operate on the regular character buffer (fp->_IO_read_ptr) instead of the actual wide-stream read pointer (fp->_wide_data->_IO_read_ptr). The program crash may happen in cases where fp->_IO_read_ptr is not initialized and hence points to NULL. The buffer under-read requires a special situation where the input character encoding is such that there are overlaps between single byte representations and multibyte representations in that encoding, resulting in spurious matches. The spurious match case is not possible in the standard Unicode character sets. Added CWE CWE-127 Added Reference https://sourceware.org/bugzilla/show_bug.cgi?id=33998