VulnerabilityPublished 29 Oct 2026

CVE-2026-96778: Pillow · Heap buffer overflow writing JPEG comment after ICC profile fills buffer

Affects aiderSource GCVE Database

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Authoritative record:CVE-2026-96778· High 7.7

Not known to be exploited · CVSS 7.7 High.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score

7.7High

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	7.7

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: Passive
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: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
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: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
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 21 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

``` ============================================================================ Heap buffer overflow writing JPEG comment after ICC profile fills buffer Location: src/libImaging/JpegEncode.c:330 in ImagingJpegEncode() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ``` A heap buffer overflow in Pillow's JPEG encoder lets anyone who can supply an image write up to 64 KB of bytes they choose, followed by the rest of the compressed image, past the end of a 64 KB heap buffer. The target is any application that re-saves the image as JPEG while keeping its colour profile. The reliable result is that the Python process is killed outright rather than raising an exception. Because the overwritten memory sits directly in front of function pointers that the encoder calls next, this could allow code execution, though the attached reproducer demonstrates only the crash. The bug is in `ImagingJpegEncode()` in `src/libImaging/JpegEncode.c`. State 4 (line 330) calls `jpeg_write_marker()` for the COM comment marker without checking that the output buffer has room. Meanwhile, `JpegImagePlugin._save()` sizes that buffer from the EXIF and ICC/XMP data only and reserves nothing for the comment. When a 65498-byte ICC profile fills the 65536-byte buffer exactly, libjpeg's `emit_byte()` stores one byte past the end and then decrements `free_in_buffer` from 0. The `size_t` counter wraps, so the marker, the comment and the entire compressed image are written out of bounds. Triggering it takes only a valid JPEG (or PNG) carrying that profile and any comment, passed through `Image.open()` and then `im.save(..., "JPEG", icc_profile=im.info.get("icc_profile"))`. That is the documented way to preserve colour. The comment is forwarded from `im.info` automatically, and no non-default setting is involved. The attached reproducer re-saves such a file on the stock build, and the process dies with SIGSEGV. An identical file without the comment saves normally. An ASan build of Pillow will not flag this, because the stray writes happen inside the system libjpeg-turbo. Valgrind does report it, as an invalid write immediately after the 65569-byte allocation. The unguarded call was introduced in e50ae85ea406 ("Use jpeg_write_marker to write comment", 2022-12-05) and first shipped in 9.4.0. ## Details `ImagingJpegEncode()` (`src/libImaging/JpegEncode.c`) is a resumable state machine that fills a caller-supplied output buffer of `bytes` bytes and returns when it is full. State 4 writes the JPEG COM marker with `jpeg_write_marker()` without first checking that the buffer has any room left. When the preceding state 3 — the verbatim copy of the "extra" APP segments (ICC profile / XMP) — ends exactly at the last byte of the buffer, `jpeg_write_marker()` is entered with `free_in_buffer == 0`. libjpeg's `emit_byte()` stores the byte first and tests `--free_in_buffer == 0` afterwards, so the `size_t` counter wraps to 2^64-1 instead of triggering the "buffer full" path, and the 4-byte marker header, the whole comment, and then (state 5) the DQT/SOF/DHT/SOS headers and the entire entropy-coded image are written linearly past the end of the 65536-byte heap buffer allocated in `src/encode.c`. A JPEG laid out as ``` FFD8 SOI FFE2 <len> "ICC_PROFILE\0" 01 01 <65498 bytes> -> im.info["icc_profile"] FFFE <len> <comment, any length 1..65533> -> im.info["comment"] <any baseline RGB JPEG body> ``` opened with `Image.open()` and re-saved with the usual colour-profile-preserving call ```python im.save(out, "JPEG", icc_profile=im.info.get("icc_profile")) ``` kills the Python process on the stock build at this commit: glibc aborts with `realloc(): invalid next size` / `corrupted size vs. prev_size`, or the process takes SIGSEGV inside `jpeg_write_marker`/`jpeg_write_scanlines`. Stopping at `JpegEncode.c:330` in gdb shows `next_output_byte - buf == 65536`, `free_in_buffer == 0`, `comment_size == 65533` before the call, and `next_output_byte - buf == 131073`, `free_in_buffer == 18446744073709486079` after it — 65537 bytes already written beyond a 65536-byte buffer before a single scanline has been encoded. An ASan build of Pillow does not flag this, because the out-of-bounds stores happen inside the (uninstrumented) system libjpeg-turbo; valgrind does, reporting `Invalid write ... 0 bytes after a block of size 65,569` from `jpeg_write_marker` called at `JpegEncode.c:330` before aborting on the corrupted heap metadata. ### Code path The buffer. `JpegImagePlugin._save()` sizes the encoder buffer from the metadata it is about to emit, allowing one spare byte after the extra block and nothing for the comment: ```python # src/PIL/JpegImagePlugin.py:859-862 else: # The EXIF info needs to be written as one block, + APP1, + one spare byte. # Ensure that our buffer is big enough. Same with the icc_profile block.

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