CVE-2026-58013 Overview
CVE-2026-58013 is a buffer over-read vulnerability in GLib, the low-level core library used by GNOME and many Linux applications. The flaw resides in the g_io_channel_read_line_backend() function inside giochannel.c. When a custom line terminator longer than one byte is configured, memcmp reads past the end of the underlying GString buffer. The condition maps to [CWE-126: Buffer Over-read].
Exploitation can leak up to 7 bytes of adjacent memory or trigger a denial of service if the over-read crosses a page boundary. GLib is bundled with Red Hat Enterprise Linux 6 through 10 and countless GNOME desktop and server applications.
Critical Impact
Network-reachable applications that call GLib I/O channel APIs with attacker-influenced line terminators can be crashed or forced to disclose small amounts of process memory.
Affected Products
- GNOME GLib (all versions prior to the upstream fix tracked in GitLab issue #3925)
- Red Hat Enterprise Linux 6, 7, 8, 9, and 10
- Downstream GNOME desktop and server applications linking against vulnerable GLib builds
Discovery Timeline
- 2026-06-30 - CVE-2026-58013 published to the National Vulnerability Database
- 2026-07-02 - Last updated in NVD database
Technical Details for CVE-2026-58013
Vulnerability Analysis
GLib provides GIOChannel, an abstraction for buffered I/O over file descriptors, sockets, and pipes. The g_io_channel_read_line_backend() routine scans the internal read buffer for a line terminator and returns the accumulated line to the caller. Applications can override the default newline terminator with g_io_channel_set_line_term(), supplying an arbitrary byte sequence.
The scanning logic invokes memcmp against the GString read buffer using the terminator length as its size argument. The comparison loop does not validate that at least terminator_length bytes remain in the buffer before dereferencing. When the terminator length exceeds one byte and the buffer holds fewer trailing bytes than that length, memcmp reads past the allocated buffer boundary.
The out-of-bounds read yields two observable outcomes. First, up to 7 bytes of adjacent heap memory may be reflected into control-flow decisions or subsequent returned data, producing an information disclosure. Second, if the over-read crosses an unmapped page boundary, the process receives SIGSEGV and terminates, resulting in denial of service.
Root Cause
The root cause is missing length validation before memcmp in giochannel.c. The function assumes the buffer contains at least terminator_length bytes without checking buf->len against that value.
Attack Vector
The attack vector is network-adjacent for any daemon that reads attacker-controlled input through a GIOChannel and uses a multi-byte custom terminator. A remote attacker who can influence the byte stream can force the buffer to end within the terminator match window, triggering the over-read on each subsequent read attempt.
See the GNOME GLib Issue #3925 and the Red Hat CVE-2026-58013 Advisory for maintainer analysis.
Detection Methods for CVE-2026-58013
Indicators of Compromise
- Repeated segmentation faults in processes that link against libglib-2.0.so, particularly those handling network input
- Core dumps whose backtraces reference g_io_channel_read_line_backend or g_io_channel_read_line
- Anomalous small memory fragments appearing in application logs or protocol responses that read past expected line boundaries
Detection Strategies
- Enable AddressSanitizer or Valgrind Memcheck in development and staging builds to catch the over-read at first occurrence
- Deploy compiler hardening (_FORTIFY_SOURCE=3, -fstack-protector-strong) so that boundary violations near page edges produce identifiable aborts
- Correlate SIGSEGV events with GLib versions across the fleet by querying package inventory data
Monitoring Recommendations
- Alert on repeated crash-restart cycles in GLib-dependent services such as gdm, NetworkManager, and GNOME session components
- Monitor auditd for anom_abend records tied to processes loading vulnerable libglib-2.0 versions
- Track network peers that consistently precede crashes to identify potential exploitation attempts
How to Mitigate CVE-2026-58013
Immediate Actions Required
- Inventory all systems running Red Hat Enterprise Linux 6 through 10 and identify installed GLib versions with rpm -q glib2
- Apply vendor updates as soon as they are published in the Red Hat and distribution security channels
- Restart long-running services that link GLib after upgrading, since the library is loaded at process start
- Restrict network exposure of daemons that call g_io_channel_set_line_term() with multi-byte terminators until patches are applied
Patch Information
Red Hat is tracking remediation through the Red Hat CVE-2026-58013 Advisory and Red Hat Bug Report #2492248. Upstream fixes are being coordinated through GNOME GLib Issue #3925. Administrators should install the patched glib2 package for their distribution once available and reboot or restart affected services.
Workarounds
- Where the application controls terminator configuration, revert to the default single-byte newline terminator until the patched GLib is installed
- Place vulnerable services behind a reverse proxy that normalizes line endings and rejects malformed protocol framing
- Apply SELinux or AppArmor confinement to limit the impact of information disclosure from affected processes
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
