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CVE-2026-27821 is a high-severity vulnerability found in GPAC, an open-source multimedia framework . The flaw is a stack-based buffer overflow located in the NHML file parser within `src/filters/dmx_nhml.c` . Specifically, when parsing an NHML file, the value of an XML attribute named `xmlHeaderEnd` is copied into a fixed-size stack buffer, `szXmlHeaderEnd
` . The vulnerable code uses the `strcpy()` function to perform this copy without any prior validation of the input's length . If a malicious actor provides an NHML file where the `xmlHeaderEnd` attribute's value exceeds 1000 bytes, `strcpy()` will write past the end of the buffer . This overflow corrupts adjacent memory on the stack, which can lead to an application crash or, under the right conditions, allow for arbitrary code execution . The issue has been patched in the GPAC GitHub repository with commit `9bd7137` . <h2 style="color: blue;">dailycve form:</h2> Platform: GPAC Version: <= 26.02.0 Vulnerability : Stack Buffer Overflow Severity: High date: 2026-02-25 <h2 style="color: blue;">Prediction: Patch already available</h2> <h2 style="color: blue;">What Undercode Say:</h2> <h2 style="color: blue;">Analytics</h2> The vulnerability was published on February 25, 2026, and last modified on March 11, 2026 . It has a CVSSv4.0 base score of 7.7 (HIGH) with the vector `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N` . The Exploit Prediction Scoring System (EPSS) probability is 0.05%, indicating a low risk of exploitation in the wild within 30 days of publication . This is a classic case of a CWE-121 stack-based buffer overflow caused by using `strcpy` instead of a bounds-checking function like `strncpy` . <h2 style="color: blue;">Bash Commands and Codes</h2> The following command can be used to check the version of GPAC installed on a system to determine if it is vulnerable: [bash] gpac -version || GPAC -v
To create a simple proof-of-concept NHML file that attempts to trigger the overflow, one could generate an `xmlHeaderEnd` string longer than 1000 bytes:
Create a string of 'A' repeated 1010 times
python3 -c 'print("A" 1010)' > overflow.txt
Craft the NHML file
echo '<?xml version="1.0"?><NHML version="1.0"><stream xmlHeaderEnd="'$(cat overflow.txt)'"/></NHML>' > poc.nhml
The vulnerable code snippet in `src/filters/dmx_nhml.c` resembles the following:
char szXmlHeaderEnd[bash]; // ... parsing logic ... // Unsafe copy from the XML attribute value (att->value) to the fixed stack buffer strcpy(szXmlHeaderEnd, att->value); // No length check
The patched code would replace this with a safe alternative, such as:
char szXmlHeaderEnd[bash]; // ... parsing logic ... strncpy(szXmlHeaderEnd, att->value, sizeof(szXmlHeaderEnd) - 1); szXmlHeaderEnd[sizeof(szXmlHeaderEnd) - 1] = '\0'; // Ensure null-termination
How Exploit
An attacker can exploit this vulnerability by crafting a malicious NHML (Nested Heterogeneous Media Language) file . The exploit does not require authentication or user interaction beyond the target system processing the file . The attacker sets the `xmlHeaderEnd` attribute in the XML to a value exceeding 1000 bytes. When GPAC’s demuxer parses this file, the oversized string is copied into the stack buffer, overwriting the return address or other critical data on the stack. This can be leveraged to redirect program execution to attacker-controlled code, leading to remote code execution (RCE) .
Protection from this CVE
The primary and most effective protection is to update GPAC to a patched version. The fix is included in versions after 26.02.0, specifically commit `9bd7137fded2db40de61a2cf3045812c8741ec52` . If an immediate update is not possible, organizations should:
1. Avoid processing untrusted or unsolicited NHML files.
- Implement network segmentation and file scanning to filter out malicious XML-based media files before they reach the GPAC application.
- Consider running GPAC in a sandboxed or containerized environment with restricted privileges to limit the impact of a potential exploit .
Impact
Successful exploitation of CVE-2026-27821 can lead to severe consequences . The primary impacts are:
– Availability (High): The most immediate impact is a denial of service, where the GPAC application crashes due to memory corruption .
– Confidentiality (None): The vulnerability itself does not directly leak information .
– Integrity (None): The vulnerability itself does not directly modify data .
– Potential for Code Execution: While not guaranteed in every exploit scenario, a stack buffer overflow is a classic memory corruption vulnerability that can often be upgraded from a simple crash to arbitrary code execution, allowing an attacker to take full control of the affected system .
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Reported By: nvd.nist.gov
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