VulnerabilityPublished 21 Oct 2026Updated 29 Oct 2026

CVE-2026-112403: Pillow · Heap buffer overflow in ImagingJpegDecode

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Authoritative record:CVE-2026-112403· Critical 9.2

Not known to be exploited · CVSS 9.2 Critical.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score

9.2Critical

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

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CVSS scores by source
CNA (GitHub_M)	CVSS 4.0	9.2

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: High
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: High
Vulnerable system availability: High
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: High: There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Homebrewaider`pkg:brew/aider`Other threats	Affected >=0.86.1_1	Fixed in–

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Description

## Summary `JpegImageFile.draft()` — which `Image.thumbnail()` calls automatically — requests 1/2, 1/4 or 1/8 scaled JPEG output and shrinks `self._size` and the tile extents to match, so `_setimage()` allocates a single-row decode buffer of `ceil(W/s)` samples. `ImagingJpegDecode()` sets `cinfo.scale_num`/`scale_denom`, calls `jpeg_start_decompress()`, and then reads scanlines into that buffer without ever comparing `cinfo.output_width`, `cinfo.output_height` or `cinfo.out_color_components` against `state->xsize`, `state->ysize` and `state->bits`. libjpeg-turbo 3.x decodes lossless (SOF3) JPEG, but hardwires lossless streams to no scaling — the requested `scale_denom` is silently discarded. It therefore returns full-width `W`-sample rows into a buffer sized for `ceil(W/s)`. Each `jpeg_read_scanlines()` call writes `(W - ceil(W/s)) x components` bytes past the end of the heap allocation, and the overflowing bytes are the decoded pixel values, which are byte-exact for an 8-bit grayscale lossless image. The input is a standards-compliant JPEG, so `Image.open(..., formats=["JPEG"])` does not prevent it. Pillow's Python SOF parser already accepts marker `0xFFC3` ("SOF3", "Spatial lossless") at 8-bit precision, so the file opens normally as a `JPEG` / mode `L` image at its full declared size. ## Affected code At `e41083f383c9cd3db95de52564cc0b6452313d4a` (`main`, 2026-08-29): - `src/libImaging/JpegDecode.c:224-262` — `ImagingJpegDecode()`; `jpeg_start_decompress()` at :240, `jpeg_read_scanlines()` at :252, with no geometry check between them. - `src/decode.c:222-231` — `_setimage()`; `state->buffer = calloc(1, state->bytes)` with `state->bytes = (state->bits * state->xsize + 7) / 8`. - `src/PIL/JpegImagePlugin.py:428-464` — `JpegImageFile.draft()`; computes `s` and shrinks `_size`, the tile extents and `decoderconfig` with no notion of lossless coding. - `src/PIL/JpegImagePlugin.py:271` — `0xFFC3: ("SOF3", "Spatial lossless", SOF)`. ```c // src/libImaging/JpegDecode.c if (context->scale > 1) { context->cinfo.scale_num = 1; context->cinfo.scale_denom = context->scale; } ... case 2: if (!jpeg_start_decompress(&context->cinfo)) { break; } state->state++; /* fall through */ case 3: ok = 1; while (state->y < state->ysize) { ok = jpeg_read_scanlines(&context->cinfo, &state->buffer, 1); ``` Because `state->ysize` (`ceil(H/s)`) can never equal libjpeg's `output_height` when `s >= 2`, the decode always ends in an error after the rows have already been written: the caller sees an exception and gets no pixels back. The `OSError` is a consequence of the overflow, not the issue being reported. ## Primitive Per scanline: a contiguous write of `(W - ceil(W/s)) x c` bytes immediately past a `calloc(ceil(W/s) x c)` block, where `c = 1` for mode `L` and 4 for RGB (RGBX) and CMYK; repeated for `ceil(H/s)` rows over the same region. The buffer size class is chosen by the attacker through `W`, and for grayscale the overflowing content is an arbitrary attacker-chosen byte string. Measured in the reproducer below: 1200x1100 mode `L`, `s=2` — a 600-byte allocation, 600 bytes written past it, ASan reporting the whole 1200-byte row write as one `memcpy`. Threshold: `draft()` must select `s >= 2`, i.e. `W // requested_w >= 2` and `H // requested_h >= 2`. For `thumbnail((256,256))` with the default `reducing_gap=2.0` that means `W, H >= 1024`. ## Reproduction Self-contained Docker reproducer (Ubuntu 24.04, clang 20, libjpeg-turbo 3.1.4 and Pillow both built from source with `-fsanitize=address`; Pillow checked out at `${TARGET_COMMIT}`, default `e41083f383c9cd3db95de52564cc0b6452313d4a`). Save the three files below as `Dockerfile`, `make_sof3.py` and `trigger.py` in an empty directory, then: ```bash docker build -t pillow-sof3-oob . && docker run --rm pillow-sof3-oob ``` `make_sof3.py` is a self-contained encoder that emits a standards-compliant 8-bit grayscale lossless-Huffman JPEG (SOI / DHT / SOF3 `P=8, Y=1100, X=1200, Nf=1` / SOS `Ss=1` predictor 1, `Se=0`, `Ah=Al=0` / entropy-coded row differences / EOI), whose rows carry a repeating marker pattern. `trigger.py` opens it and calls `thumbnail()`, whose implicit `draft()` picks `s=2` and allocates a 600-byte row buffer. ### `Dockerfile` ```dockerfile FROM ubuntu:24.04 ENV DEBIAN_FRONTEND=noninteractive ARG TARGET_COMMIT=e41083f383c9cd3db95de52564cc0b6452313d4a ARG CLANG_VERSION=20 ARG LIBJPEG_TURBO_TAG=3.1.4 RUN apt-get update && apt-get install -y --no-install-recommends \ ca-certificates git make cmake nasm pkg-config libc6-dev gcc \ wget gnupg lsb-release software-properties-common \ python3 python3-dev python3-pip python3-venv zlib1g-dev \ && wget -qO /tmp/llvm.sh https://apt.llvm.org/llvm.sh && chmod +x /tmp/llvm.sh && /tmp/llvm.sh ${CLANG_VERSION} \

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