Bug 2537748 (CVE-2026-95508)

Summary: CVE-2026-95508 libslirp: libslirp: heap buffer overflow in DHCPv6/TFTP response builders on small interface MTU
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A heap-based buffer overflow was found in the DHCPv6 and TFTP response builders of libslirp. When the host is configured with a small interface MTU, a guest-supplied DHCPv6 CLIENTID option or TFTP blksize option can overflow the reply buffer with attacker-controlled content and length, resulting in denial of service and potentially arbitrary code execution in the host process. The default interface MTU is not affected.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2537751    
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Description OSIDB Bzimport 2026-09-22 07:30:07 UTC 
A flaw was found in libslirp. The DHCPv6 (src/dhcpv6.c) and TFTP (src/tftp.c) response builders write guest-influenced, variable-length data into a reply mbuf sized according to SlirpConfig.if_mtu, without checking that the write stays within that buffer. In dhcpv6_info_request(), a guest-supplied DHCPv6 CLIENTID option (up to 256 bytes, capped independently of if_mtu) is memcpy'd into the reply with no bounds check against the mbuf's actual size, overflowing the heap buffer whenever if_mtu is smaller than the client_id length plus fixed overhead. A related sink in the same function computes a signed 'smaxlen' for the boot-file-URL option that can go negative once earlier options have consumed the MTU window, which, when passed as an unsigned size to slirp_fmt(), defeats its length truncation entirely. An analogous pattern exists in tftp_read_data() (src/tftp.c) via the guest-supplied blksize option. These sinks are only reachable when the host/hypervisor operator has configured a small interface MTU (below the IPv6 minimum link MTU of 1280, down to the library's accepted floor of 68); the default MTU of 1500 is not affected.