CVE-2026-5928Potential buffer under-read in ungetwc
Updated under an hour ago ()
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It affects The GNU C Library glibc and 4 other products. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 7.5 HIGH (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Weakness (CWE)
- CWE-127
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- glibc
- NVD analysis
- Modified
- Record last updated
- Oct 15, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
The GNU C Library glibc gnu_c_library:glibc (from the name) | from 2.1.1-89 through 2.43 | CNA record |
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518_4_pn_dp_mfp (from the name) | from V3.1.5 before V3.1.6 | CISA ADP |
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518f_4_pn_dp_mfp (from the name) | from V3.1.5 before V3.1.6 | CISA ADP |
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP siemens:siplus_s7_1500_cpu_1518_4_pn_dp_mfp (from the name) | from V3.1.5 before V3.1.6 | CISA ADP |
gnu glibc gnu:glibc | through 2.43 | NVD |
References
- https://sourceware.org/bugzilla/show_bug.cgi?id=33998exploit, issue-tracking
- https://cert-portal.siemens.com/productcert/html/ssa-082556.html
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.