Bug 2526301

Summary: CVE-2026-18374 zig: glibc: Heap buffer overflow via attacker-controlled fopen mode string [fedora-all]
Product: [Fedora] Fedora Reporter: Ganesh <gnaik>
Component: zigAssignee: Jan Drögehoff <sentrycraft123>
Status: CLOSED NOTABUG QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: rawhideCC: alebastr89, baltevl, josherna, marko03kostic, purin21345, renich, sentrycraft123, suraj.ghimire7
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["7dfb1b13-46a5-4d39-933c-75cda64a755a"]}
Fixed In Version: Doc Type: ---
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2026-09-01 07:13:44 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 2525256    

Description Ganesh 2026-08-31 14:05:31 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

Passing an effectively empty string to the `,ccs=` syntax extension of the mode argument in the `fopen` function in the GNU C Library version 2.45 or earlier may result in a heap buffer overflow when the mode string input to the function is attacker controlled.



This usage pattern is not seen in applications in common GNU/Linux distributions and applications that process user-supplied values for `ccs` should not pass them through without validation.
Comment 1 Renich Bon Ciric 2026-09-01 07:13:44 UTC 
Zig is not affected by this vulnerability.

While `zig.spec` declares `Provides: bundled(glibc) = 2.43` to account for embedded headers and ABI symbol metadata, Zig does not bundle or compile the GNU C Library implementation of `fopen` (or `libio` where the `,ccs=` parsing flaw resides).

Specifically:

- Zig only ships glibc ABI symbol tables (`abilists`) to generate compile-time dynamic linking stubs (`.so`), generic headers, and minimal C runtime startup objects (`crt1.o`, `elf-init`, `stat` shims).

- Zig compiler binaries and generated executables dynamically link against the host/target system's runtime `libc.so.6`.

Closing as NOTABUG.