Bug 2501564 (CVE-2026-13713)

Summary: CVE-2026-13713 YAML-Syck: YAML::Syck: Denial of Service via crafted YAML document
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in YAML::Syck. This vulnerability allows a remote attacker to cause a denial of service (DoS) by providing a specially crafted YAML document. The flaw occurs due to a use-after-free and double-free condition when an anchor node is redefined while still on the parser's value stack, leading to the interpreter crashing.
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Bug Depends On: 2501656, 2501657    
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Description OSIDB Bzimport 2026-07-16 22:01:34 UTC 
YAML::Syck versions before 1.47 for Perl allow a use-after-free and double-free via an anchor node freed while still on the parser value stack.

In the bundled libsyck, when an anchor name is redefined or removed, syck_hdlr_add_anchor and syck_hdlr_remove_anchor free the node stored under that name with syck_free_node. That node can still be live on the parser's value stack, so syck_hdlr_add_node reaches it again and frees it a second time. On a normal build the 48-byte node chunk is freed twice and the interpreter aborts. Anchors need no special flags, so this is reached on the default Load path, and a 7-byte document that redefines an anchor triggers it.

Any caller that runs Load or LoadFile on an untrusted document that redefines an anchor mid-parse crashes the interpreter, a denial of service.