CVE-2026-76220VulnerabilityPublished 20 Aug 2026Updated 26 Oct 2026

shallow-backup · GitPython: Unsafe git option guard bypass via split_single_char_options=False short-option token smuggling enables

Affects shallow-backupSource GCVE Database

Authoritative record:CVE-2026-76220· High 8.7

Not known to be exploited · CVSS 8.7 High : upgrade to 6.6_6 soon.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 4.0 base score

8.7High

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

EPSS: 0.9% chance of exploitation in 30 days – higher than 59% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.6_6

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: Low
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: 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: 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: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
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 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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

Upgrade shallow-backup to 6.6_6.

Affected software

Product	Affected	Fixed in
Homebrewshallow-backup`pkg:brew/shallow-backup`Other threats	Affected >=5.0.1 <6.6_6	Fixed in 6.6_6

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

## Summary The `check_unsafe_options` guard can be bypassed on every guarded method (clone/clone_from, fetch/pull/push, ls_remote, iter_commits, blame, archive) by combining a single-character kwarg with `split_single_char_options=False`. The guard's candidate list omits the smuggled option, but `transform_kwarg` emits a JOINED `-n<value>` argv token that git parses as `--upload-pack=<cmd>`, yielding arbitrary command execution at the default `allow_unsafe_options=False`. This is an incomplete-fix bypass of commit `e8d0fbf7` (the fix for GHSA-r9mr-m37c-5fr3), which only emits value-derived candidates when `split_single_char_options` is True. ## Root Cause `_option_candidates` derives value-token candidates only under `if len(key)==1 and split_single_char_options:` (cmd.py:1048, added by `e8d0fbf7`). With `split_single_char_options=False`, `_option_candidates([], {"n":"utouch <cmd>;git-upload-pack"})` returns only `['-n']` (not on the denylist), so the guard passes. But `transform_kwarg('n', value, split_single_char_options=False)` emits the JOINED token `-nutouch <cmd>;git-upload-pack` (cmd.py:1631). git clusters value-less short flags then parses `-u<cmd>` = `--upload-pack=<cmd>` → command execution. The hardened guard WOULD block the joined token if it saw it — the flaw is it never receives it. ## Impact Arbitrary OS command execution as the host process (via `--upload-pack`) at default `allow_unsafe_options=False`, affecting all guarded methods that forward kwargs. Precondition: the app forwards a user-controlled kwargs dict containing `split_single_char_options=False` plus a single-char key (same user-dict-forwarding model GHSA-r9mr-m37c-5fr3 accepts). ## Proof of Concept ```python from git import Repo Repo.clone_from(src, dst, n="utouch /tmp/ACE;git-upload-pack", split_single_char_options=False) # /tmp/ACE created -> ACE ``` ## Attack Chain 1. Entry: app forwards user kwargs to `Repo.clone_from(url, path, **kwargs)`: `{split_single_char_options: False, n: 'utouch /tmp/ACE;git-upload-pack'}`. 2. Check: `check_unsafe_options(_option_candidates([], kwargs), unsafe_git_clone_options)`. Guard: denylist includes `--upload-pack`/`-u`. Bypass proof: `_option_candidates` yields only `['-n']` (value token skipped because `split=False`); guard never sees `-u`. 3. Sink: `transform_kwarg` emits joined token (cmd.py:1631). argv (observed): `['git','clone','-v','-nutouch /tmp/ACE;git-upload-pack','--','<src>','<dst>']`. 4. Impact: git clusters `-n` + `-u<cmd>` → runs upload-pack command → ACE. ## Bypass Evidence Independently reproduced (gate harness, default `allow_unsafe_options=False`): the `split=False` payload created the marker `VH05_GATE_ACE` (ACE); the clone returned normally (guard bypassed). Control: `n='--upload-pack=…'` (split default True) → `UnsafeOptionError: --upload-pack is not allowed`. Fix-commit read: `e8d0fbf7` extends candidates only under `if len(key)==1 and split_single_char_options:` — split=False skips value emission. Also confirmed the earlier clustering-parse fix (commit `56806080`) does not cover this because the guard only ever receives `['-n']`. ## Affected Versions `GitPython <= 3.1.57` (code present verbatim on the latest release tag). ## Suggested Fix Make `_option_candidates` emit value-derived candidates regardless of `split_single_char_options` (i.e. also for the joined `-n<value>` form), OR run `check_unsafe_options` over the fully-transformed argv rather than the reconstructed name-only candidate list. --- Reported by **zx (Jace)** — GitHub: @manus-use

References

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