CVE-2026-58082 in iconv
Summary
by MITRE • 08/19/2026
The ISO-2022 encoding module used a stack buffer sized to MB_LEN_MAX (6 bytes) for intermediate character output. Some ISO-2022 variants can require up to 10 bytes per character, in which case conversions can trigger a stack buffer overflow of up to four bytes.
An application that uses iconv(3) to convert untrusted input to or from one of the affected encodings may be vulnerable to buffer overflows if it uses one of the affected encoding modules.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified in this context stems from a fundamental implementation error within the ISO-2022 character encoding module, specifically regarding how intermediate character output buffers are allocated on the stack. The core technical flaw lies in the assumption that all variants of the ISO-2022 standard can be represented using a maximum buffer size defined by MB_LEN_MAX, which is set to six bytes. This allocation strategy fails to account for specific edge cases within certain ISO-2022 variants where character sequences may require up to ten bytes for proper representation during conversion processes. When an application attempts to convert untrusted input that triggers these longer sequence requirements, the fixed-size stack buffer proves insufficient, resulting in a write operation that exceeds the allocated memory boundaries by up to four bytes. This constitutes a classic stack-based buffer overflow condition where data is written beyond the bounds of the intended variable, potentially overwriting adjacent memory locations on the call stack including return addresses and saved frame pointers.
From an operational perspective, this vulnerability poses significant risks to any software system that relies on the iconv library for character set conversions involving ISO-2022 encodings. Since iconv is a widely used standard interface in Unix-like operating systems for text encoding translation, applications ranging from web servers processing internationalized content to email clients handling legacy message formats are potentially exposed if they utilize affected encoding modules without proper input validation or bounds checking. An attacker who can supply crafted malicious input containing specific ISO-2022 sequences could exploit this buffer overflow to achieve arbitrary code execution with the privileges of the vulnerable application. The impact extends beyond simple denial of service through crashes, as precise control over the overwritten stack data allows for sophisticated exploitation techniques that bypass standard memory protection mechanisms if they are not fully enabled or configured correctly on the target system.
This vulnerability aligns closely with Common Weakness Enumeration category CWE-121, which describes a stack-based buffer overflow resulting from insufficient bounds checking during input processing. The attack vector typically involves providing specially crafted data to an application that performs encoding conversions, placing it within the scope of CWE-20 Improper Input Validation when considering how the system fails to verify if the incoming character sequence fits within the pre-allocated buffer space. In terms of adversarial tactics, this flaw facilitates techniques associated with MITRE ATT&CK subcategory T1190 Exploit Public-Facing Application, as it allows attackers to leverage a known weakness in a common library component that is often exposed through network services or user-facing interfaces that accept text input for processing and display.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary solution involves updating the underlying iconv implementation or the specific ISO-2022 encoding module to dynamically allocate buffers based on the actual maximum byte length required by the target character set variant, rather than relying on a static MB_LEN_MAX value that may be too small for certain edge cases. Developers integrating these libraries should implement strict input validation mechanisms to detect and reject sequences that exceed expected lengths before conversion attempts are made. Furthermore, enabling modern compiler security features such as stack canaries, Address Space Layout Randomization (ASLR), and Non-Executable Stack (NX) bits provides critical layers of defense-in-depth that can mitigate the impact of exploitation even if the underlying buffer overflow vulnerability is present in older or unpatched versions of the software.